diff --git a/src/components/BacklogCard.jsx b/src/components/BacklogCard.jsx
index 8e5f532..b345e9f 100644
--- a/src/components/BacklogCard.jsx
+++ b/src/components/BacklogCard.jsx
@@ -10,7 +10,7 @@ import {Select, SelectContent, SelectItem, SelectTrigger, SelectValue} from '@/c
 import {Textarea} from '@/components/ui/textarea';
 import {cn} from '@/lib/utils';
 import {STATUS_META} from './GameStatusBadge.jsx';
-import {NO_PRIORITY, saveBacklogEntry, toBacklogRequest} from '../utils/backlog.js';
+import {changedFields, NO_PRIORITY, saveBacklogEntry} from '../utils/backlog.js';
 import {GAME_PRIORITIES, GAME_STATUSES, MAX_NOTES_LENGTH} from '../utils/limits.js';
 import useUnsavedChanges from '../hooks/useUnsavedChanges.js';
 
@@ -33,14 +33,15 @@ export default function BacklogCard({game, onSaved}) {
     }, [game.status]);
     const [busy, setBusy] = useState(false);
 
-    const dirty = JSON.stringify(form) !== JSON.stringify(saved);
+    const changes = changedFields(saved, form);
+    const dirty = Object.keys(changes).length > 0;
     useUnsavedChanges(dirty);
     const set = (field) => (value) => setForm((f) => ({...f, [field]: value}));
 
     const save = async () => {
         setBusy(true);
         try {
-            const response = await saveBacklogEntry(game.appid, toBacklogRequest(form));
+            const response = await saveBacklogEntry(game.appid, changes);
             if (response.status === 401) return;
             if (!response.ok) {
                 toast.error(t('BACKLOG.SAVE_FAILED'));
@@ -67,72 +68,75 @@ export default function BacklogCard({game, onSaved}) {
                 {t('BACKLOG.TITLE')}
             </h2>
 
-            <div className="grid gap-5 sm:grid-cols-3">
-                <div className="space-y-2">
-                    <Label htmlFor="backlog-status">{t('BACKLOG.STATUS_LABEL')}</Label>
-                    <Select value={form.status} onValueChange={set('status')}>
-                        <SelectTrigger id="backlog-status" className="w-full"><SelectValue/></SelectTrigger>
-                        <SelectContent>
-                            {GAME_STATUSES.map((s) => {
-                                const {icon: Icon, text} = STATUS_META[s];
-                                return (
-                                    <SelectItem key={s} value={s}>
-                                        <Icon className={text}/>
-                                        {t(`BACKLOG.STATUS.${s}`)}
-                                    </SelectItem>
-                                );
-                            })}
-                        </SelectContent>
-                    </Select>
-                </div>
+            {/* Locked while saving: the answer replaces the form, so an edit made meanwhile would be lost. */}
+            <fieldset disabled={busy} className="contents">
+                <div className="grid gap-5 sm:grid-cols-3">
+                    <div className="space-y-2">
+                        <Label htmlFor="backlog-status">{t('BACKLOG.STATUS_LABEL')}</Label>
+                        <Select value={form.status} onValueChange={set('status')}>
+                            <SelectTrigger id="backlog-status" className="w-full"><SelectValue/></SelectTrigger>
+                            <SelectContent>
+                                {GAME_STATUSES.map((s) => {
+                                    const {icon: Icon, text} = STATUS_META[s];
+                                    return (
+                                        <SelectItem key={s} value={s}>
+                                            <Icon className={text}/>
+                                            {t(`BACKLOG.STATUS.${s}`)}
+                                        </SelectItem>
+                                    );
+                                })}
+                            </SelectContent>
+                        </Select>
+                    </div>
 
-                <div className="space-y-2">
-                    <Label htmlFor="backlog-priority">{t('BACKLOG.PRIORITY_LABEL')}</Label>
-                    <Select value={form.priority} onValueChange={set('priority')}>
-                        <SelectTrigger id="backlog-priority" className="w-full"><SelectValue/></SelectTrigger>
-                        <SelectContent>
-                            <SelectItem value={NO_PRIORITY}>{t('BACKLOG.PRIORITY.NONE')}</SelectItem>
-                            {GAME_PRIORITIES.map((p) => (
-                                <SelectItem key={p} value={p}>{t(`BACKLOG.PRIORITY.${p}`)}</SelectItem>
+                    <div className="space-y-2">
+                        <Label htmlFor="backlog-priority">{t('BACKLOG.PRIORITY_LABEL')}</Label>
+                        <Select value={form.priority} onValueChange={set('priority')}>
+                            <SelectTrigger id="backlog-priority" className="w-full"><SelectValue/></SelectTrigger>
+                            <SelectContent>
+                                <SelectItem value={NO_PRIORITY}>{t('BACKLOG.PRIORITY.NONE')}</SelectItem>
+                                {GAME_PRIORITIES.map((p) => (
+                                    <SelectItem key={p} value={p}>{t(`BACKLOG.PRIORITY.${p}`)}</SelectItem>
+                                ))}
+                            </SelectContent>
+                        </Select>
+                    </div>
+
+                    <div className="space-y-2">
+                        <Label id="backlog-rating">{t('BACKLOG.RATING_LABEL')}</Label>
+                        <div role="group" aria-labelledby="backlog-rating" className="flex h-9 items-center gap-1">
+                            {[1, 2, 3, 4, 5].map((n) => (
+                                <button
+                                    key={n}
+                                    type="button"
+                                    aria-label={t('BACKLOG.RATING_STARS', {count: n})}
+                                    aria-pressed={form.rating === n}
+                                    onClick={() => set('rating')(form.rating === n ? 0 : n)}
+                                    className="rounded-sm p-0.5 outline-none focus-visible:ring-[3px] focus-visible:ring-ring/50"
+                                >
+                                    <Star className={cn('size-6 transition-colors',
+                                        n <= form.rating ? 'fill-amber-400 text-amber-400' : 'text-muted-foreground/40 hover:text-amber-400')}/>
+                                </button>
                             ))}
-                        </SelectContent>
-                    </Select>
-                </div>
-
-                <div className="space-y-2">
-                    <Label id="backlog-rating">{t('BACKLOG.RATING_LABEL')}</Label>
-                    <div role="group" aria-labelledby="backlog-rating" className="flex h-9 items-center gap-1">
-                        {[1, 2, 3, 4, 5].map((n) => (
-                            <button
-                                key={n}
-                                type="button"
-                                aria-label={t('BACKLOG.RATING_STARS', {count: n})}
-                                aria-pressed={form.rating === n}
-                                onClick={() => set('rating')(form.rating === n ? 0 : n)}
-                                className="rounded-sm p-0.5 outline-none focus-visible:ring-[3px] focus-visible:ring-ring/50"
-                            >
-                                <Star className={cn('size-6 transition-colors',
-                                    n <= form.rating ? 'fill-amber-400 text-amber-400' : 'text-muted-foreground/40 hover:text-amber-400')}/>
-                            </button>
-                        ))}
+                        </div>
                     </div>
                 </div>
-            </div>
 
-            <div className="space-y-2">
-                <div className="flex items-baseline justify-between">
-                    <Label htmlFor="backlog-notes">{t('BACKLOG.NOTES_LABEL')}</Label>
-                    <span className="text-xs text-muted-foreground tabular-nums">{form.notes.length} / {MAX_NOTES_LENGTH}</span>
+                <div className="space-y-2">
+                    <div className="flex items-baseline justify-between">
+                        <Label htmlFor="backlog-notes">{t('BACKLOG.NOTES_LABEL')}</Label>
+                        <span className="text-xs text-muted-foreground tabular-nums">{form.notes.length} / {MAX_NOTES_LENGTH}</span>
+                    </div>
+                    <Textarea
+                        id="backlog-notes"
+                        rows={3}
+                        maxLength={MAX_NOTES_LENGTH}
+                        placeholder={t('BACKLOG.NOTES_PLACEHOLDER')}
+                        value={form.notes}
+                        onChange={(e) => set('notes')(e.target.value)}
+                    />
                 </div>
-                <Textarea
-                    id="backlog-notes"
-                    rows={3}
-                    maxLength={MAX_NOTES_LENGTH}
-                    placeholder={t('BACKLOG.NOTES_PLACEHOLDER')}
-                    value={form.notes}
-                    onChange={(e) => set('notes')(e.target.value)}
-                />
-            </div>
+            </fieldset>
 
             <div className="flex justify-end gap-2">
                 <Button variant="ghost" onClick={() => setForm(saved)} disabled={!dirty || busy}>
diff --git a/src/components/BacklogCard.test.jsx b/src/components/BacklogCard.test.jsx
index 05c2f4b..438445a 100644
--- a/src/components/BacklogCard.test.jsx
+++ b/src/components/BacklogCard.test.jsx
@@ -1,6 +1,6 @@
 // @vitest-environment jsdom
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
-import {cleanup, fireEvent, render, screen, waitFor} from '@testing-library/react';
+import {act, cleanup, fireEvent, render, screen, waitFor} from '@testing-library/react';
 import {MemoryRouter} from 'react-router-dom';
 import {fetchRoutes, json} from '../test/fetchRoutes.js';
 import BacklogCard from './BacklogCard.jsx';
@@ -14,7 +14,8 @@ const saveButton = () => screen.getByRole('button', {name: 'BACKLOG.SAVE'});
 describe('BacklogCard', () => {
     beforeEach(() => {
         localStorage.setItem('tbp_session', '1');
-        fetchRoutes({'PUT /api/library/games/220/backlog': (url, init) => json(200, JSON.parse(init.body))});
+        // Core answers the whole entry; the fields not sent come from the server.
+        fetchRoutes({'PATCH /api/library/games/220/backlog': (url, init) => json(200, {...game, ...JSON.parse(init.body)})});
     });
 
     afterEach(() => {
@@ -42,8 +43,44 @@ describe('BacklogCard', () => {
         await waitFor(() => expect(onSaved).toHaveBeenCalled());
         const [url, init] = fetch.mock.calls[0];
         expect(url).toMatch(/\/api\/library\/games\/220\/backlog$/);
-        expect(init.method).toBe('PUT');
-        expect(JSON.parse(init.body)).toEqual({status: 'PLAYING', rating: null, notes: null, priority: null});
+        expect(init.method).toBe('PATCH');
+        expect(JSON.parse(init.body)).toEqual({rating: null, notes: null});
+        expect(saveButton().disabled).toBe(true);
+    });
+
+    it('sends only the changed notes, so an older tab does not overwrite the other fields', async () => {
+        const onSaved = vi.fn();
+        render(<MemoryRouter><BacklogCard game={game} onSaved={onSaved}/></MemoryRouter>);
+
+        fireEvent.change(screen.getByRole('textbox'), {target: {value: 'new notes'}});
+        fireEvent.click(saveButton());
+
+        await waitFor(() => expect(onSaved).toHaveBeenCalled());
+        expect(JSON.parse(fetch.mock.calls[0][1].body)).toEqual({notes: 'new notes'});
+    });
+
+    it('locks the fields while the save runs, so nothing typed then is lost', async () => {
+        let answer;
+        fetchRoutes({'PATCH /api/library/games/220/backlog': (url, init) => new Promise((resolve) => {
+            answer = () => resolve(json(200, {...game, ...JSON.parse(init.body)}));
+        })});
+        render(<MemoryRouter><BacklogCard game={game}/></MemoryRouter>);
+
+        fireEvent.click(screen.getByRole('button', {name: 'BACKLOG.RATING_STARS:5'}));
+        fireEvent.click(saveButton());
+
+        // :disabled, not .disabled: the fieldset locks them, not their own attribute.
+        expect(screen.getByRole('textbox').matches(':disabled')).toBe(true);
+        expect(screen.getByRole('button', {name: 'BACKLOG.RATING_STARS:1'}).matches(':disabled')).toBe(true);
+        await act(async () => answer());
+        expect(screen.getByRole('textbox').matches(':disabled')).toBe(false);
+    });
+
+    it('does not count blank notes instead of none as a change', () => {
+        render(<MemoryRouter><BacklogCard game={{...game, notes: null}}/></MemoryRouter>);
+
+        fireEvent.change(screen.getByRole('textbox'), {target: {value: '   '}});
+
         expect(saveButton().disabled).toBe(true);
     });
 });
diff --git a/src/components/PlayingHint.jsx b/src/components/PlayingHint.jsx
index e4982d4..dc0c280 100644
--- a/src/components/PlayingHint.jsx
+++ b/src/components/PlayingHint.jsx
@@ -5,7 +5,7 @@ import {Gamepad2, Loader2} from 'lucide-react';
 
 import {Button} from '@/components/ui/button';
 import {Card} from '@/components/ui/card';
-import {saveBacklogEntry} from '../utils/backlog.js';
+import {saveGameStatus} from '../utils/backlog.js';
 import {formatPlaytime} from '../utils/games.js';
 
 /**
@@ -22,9 +22,7 @@ export default function PlayingHint({game, onChanged}) {
     const setPlaying = async () => {
         setBusy(true);
         try {
-            const response = await saveBacklogEntry(game.appid, {
-                status: 'PLAYING', rating: game.rating ?? null, notes: game.notes ?? null, priority: game.priority ?? null,
-            });
+            const response = await saveGameStatus(game.appid, 'PLAYING');
             if (response.status === 401) return;
             if (!response.ok) {
                 toast.error(t('BACKLOG.SAVE_FAILED'));
diff --git a/src/components/PlayingHint.test.jsx b/src/components/PlayingHint.test.jsx
index 62a35fb..bc9bdcb 100644
--- a/src/components/PlayingHint.test.jsx
+++ b/src/components/PlayingHint.test.jsx
@@ -14,7 +14,8 @@ const renderHint = (props) => render(<MemoryRouter><PlayingHint game={game} onCh
 describe('PlayingHint', () => {
     beforeEach(() => {
         localStorage.setItem('tbp_session', '1');
-        fetchRoutes({'PUT /api/library/games/220/backlog': (url, init) => json(200, JSON.parse(init.body))});
+        // Core changes only the status and answers the whole entry.
+        fetchRoutes({'PUT /api/library/games/220/status': (url, init) => json(200, {...game, ...JSON.parse(init.body)})});
     });
 
     afterEach(() => {
@@ -31,15 +32,15 @@ describe('PlayingHint', () => {
         expect(screen.queryByRole('button')).toBeNull();
     });
 
-    it('sets the game to PLAYING and keeps the other fields', async () => {
+    it('sends only the status, so Core keeps the other fields', async () => {
         const onChanged = vi.fn();
         renderHint({onChanged});
 
         fireEvent.click(screen.getByRole('button', {name: 'GAME_DETAIL.SET_PLAYING'}));
 
-        await waitFor(() => expect(onChanged).toHaveBeenCalledWith({status: 'PLAYING', rating: 3, notes: 'keep', priority: 'HIGH'}));
+        await waitFor(() => expect(onChanged).toHaveBeenCalledWith(expect.objectContaining({status: 'PLAYING'})));
         const [url, init] = fetch.mock.calls[0];
-        expect(url).toMatch(/\/api\/library\/games\/220\/backlog$/);
-        expect(JSON.parse(init.body)).toEqual({status: 'PLAYING', rating: 3, notes: 'keep', priority: 'HIGH'});
+        expect(url).toMatch(/\/api\/library\/games\/220\/status$/);
+        expect(JSON.parse(init.body)).toEqual({status: 'PLAYING'});
     });
 });
diff --git a/src/pages/GameDetail.test.jsx b/src/pages/GameDetail.test.jsx
index ec53cce..b0be9ab 100644
--- a/src/pages/GameDetail.test.jsx
+++ b/src/pages/GameDetail.test.jsx
@@ -116,7 +116,8 @@ describe('GameDetail', () => {
         });
 
     it('keeps unsaved notes in the backlog card when the hint sets the game to playing', async () => {
-        answer(game, {'PUT /api/library/games/220/backlog': echo});
+        // Core changes only the status and answers the whole entry.
+        answer(game, {'PUT /api/library/games/220/status': (url, init) => json(200, {...game, ...JSON.parse(init.body)})});
         renderDetail();
         const notes = await screen.findByLabelText('BACKLOG.NOTES_LABEL');
         fireEvent.change(notes, {target: {value: 'my draft'}});
diff --git a/src/utils/backlog.js b/src/utils/backlog.js
index 4fe935d..4e16b90 100644
--- a/src/utils/backlog.js
+++ b/src/utils/backlog.js
@@ -14,15 +14,24 @@ export const toBacklogRequest = ({status, rating, notes, priority}) => ({
 });
 
 /**
- * PUT /api/library/games/{appid}/backlog. The caller handles the response status.
- *
- * @param entry a backlog entry in request form, see toBacklogRequest
+ * The fields of `form` that differ from `saved`, in request form: what saveBacklogEntry sends.
  */
-export const saveBacklogEntry = (appid, entry) =>
+export const changedFields = (saved, form) => {
+    const before = toBacklogRequest(saved);
+    return Object.fromEntries(Object.entries(toBacklogRequest(form)).filter(([field, value]) => value !== before[field]));
+};
+
+/**
+ * PATCH /api/library/games/{appid}/backlog with only the changed fields, so an older tab keeps the newer ones; null
+ * clears a field. Answers the whole entry. The caller handles the response status.
+ *
+ * @param changes see changedFields
+ */
+export const saveBacklogEntry = (appid, changes) =>
     apiFetch(`${import.meta.env.VITE_CORE_API_URL}/api/library/games/${appid}/backlog`, {
-        method: 'PUT',
+        method: 'PATCH',
         headers: {'Content-Type': 'application/json'},
-        body: JSON.stringify(entry),
+        body: JSON.stringify(changes),
     });
 
 /**