diff --git a/components/calendar/calendar-app.tsx b/components/calendar/calendar-app.tsx
index b824e25a8..ede2678b5 100644
--- a/components/calendar/calendar-app.tsx
+++ b/components/calendar/calendar-app.tsx
@@ -124,6 +124,8 @@ export function CalendarApp({ linkSegments: routeSegments }: CalendarAppProps =
   const isMobile = useIsMobile();
   const isDesktop = useIsDesktop();
   const isEmbedded = useIsEmbedded();
+  // The Pro interface takes over this route; the Pro tab loads the data then.
+  const proInterfaceActive = useProInterfaceActive();
   // Mountain View's desktop chrome: its top bar in place of the left rail.
   const mvShell = useMountainViewShell(isEmbedded);
   // When the pane (Pro shell) or window is narrower than `lg`, the sidebar
@@ -364,14 +366,17 @@ export function CalendarApp({ linkSegments: routeSegments }: CalendarAppProps =
   // Single-account fetch path. The Pro shell aggregates calendars from
   // every connected account via [[useProMultiAccountCalendars]] below, so
   // skip this fetch there to avoid clobbering the merged list with the
-  // active client's calendars only.
+  // active client's calendars only. That includes the standard instance
+  // that renders while the Pro interface takes over the route: its raw ids
+  // replaced the merged list after the Pro tab loaded it, and the selection
+  // the user made in between went to another account's calendar.
   useEffect(() => {
-    if (isEmbedded) return;
+    if (isEmbedded || proInterfaceActive) return;
     if (client && !hasFetched.current) {
       hasFetched.current = true;
       fetchCalendars(client);
     }
-  }, [client, fetchCalendars, isEmbedded]);
+  }, [client, fetchCalendars, isEmbedded, proInterfaceActive]);
 
   // Auto-refresh iCal subscriptions
   useEffect(() => {
@@ -496,11 +501,11 @@ export function CalendarApp({ linkSegments: routeSegments }: CalendarAppProps =
   }, [client, enableCalendarTasks, normalizedViewMode, showTasksOnCalendar, fetchTasksFn]);
 
   useEffect(() => {
-    if (isEmbedded) return;
+    if (isEmbedded || proInterfaceActive) return;
     if (client && calendars.length > 0 && dateRange) {
       fetchEvents(client, dateRange.start, dateRange.end);
     }
-  }, [client, calendars.length, dateRange, fetchEvents, isEmbedded]);
+  }, [client, calendars.length, dateRange, fetchEvents, isEmbedded, proInterfaceActive]);
 
   // Pro shell only: aggregate calendars and events from every connected
   // account so the sidebar lists them all (and the views render their
@@ -851,7 +856,6 @@ export function CalendarApp({ linkSegments: routeSegments }: CalendarAppProps =
   // The permalink for what the calendar is currently showing. In the Pro
   // shell only the focused tab writes the address bar; the standard instance
   // that renders while Pro takes over a route stays silent.
-  const proInterfaceActive = useProInterfaceActive();
   const isFocusedProTab = useIsFocusedProTab();
   const isPaneScoped = useIsPaneScoped();
   const eventLinkId = showEventModal && editEvent ? editEvent.id : null;
@@ -933,7 +937,7 @@ export function CalendarApp({ linkSegments: routeSegments }: CalendarAppProps =
     onRefresh: async () => {
       if (!client) return;
       const calendarRefresh = multiAccountEnabled && accountClients.length > 0 && activeAccountId
-        ? fetchAllAccountsCalendarsFn(accountClients)
+        ? fetchAllAccountsCalendarsFn(accountClients, activeAccountId)
         : fetchCalendars(client);
       await Promise.all([
         calendarRefresh,
diff --git a/hooks/use-pro-multi-account-calendars.ts b/hooks/use-pro-multi-account-calendars.ts
index 2acac5ff7..7db808cce 100644
--- a/hooks/use-pro-multi-account-calendars.ts
+++ b/hooks/use-pro-multi-account-calendars.ts
@@ -49,7 +49,7 @@ export function useProMultiAccountCalendars(start: string | null, end: string |
   // bootstrapping).
   useEffect(() => {
     if (!enabled || !activeAccountId || accountClients.length === 0) return;
-    void fetchAllAccountsCalendars(accountClients);
+    void fetchAllAccountsCalendars(accountClients, activeAccountId);
   }, [enabled, activeAccountId, accountClients, fetchAllAccountsCalendars]);
 
   // Fetch events for the current visible date range across all accounts.
diff --git a/stores/__tests__/calendar-selection-after-fetch.test.ts b/stores/__tests__/calendar-selection-after-fetch.test.ts
index a0afa4654..4783f78cf 100644
--- a/stores/__tests__/calendar-selection-after-fetch.test.ts
+++ b/stores/__tests__/calendar-selection-after-fetch.test.ts
@@ -115,3 +115,21 @@ describe('reconcileSelectedIds with unloaded accounts', () => {
     expect(reconcileSelectedIds(['B@h::b'], calendars)).toEqual(['A@h::b']);
   });
 });
+
+// Stalwart gives every account's default calendar the same id ("b"). The
+// raw ids a single-account load selected are the active login's; turning to
+// the merged list mapped them onto whichever account sorted first, so the
+// active account's calendars went hidden and another's showed.
+describe('raw selected ids when the merged list loads', () => {
+  it("map onto the active login's calendars", async () => {
+    useCalendarStore.setState({ calendars: [], selectedCalendarIds: ['b', 'ca:b'] });
+    const list = () => clientReturning({ calendars: [cal({ id: 'b', accountId: 'x' }), cal({ id: 'ca:b', accountId: 'ca', isShared: true })] });
+
+    await useCalendarStore.getState().fetchAllAccountsCalendars(
+      [{ localAccountId: 'A@h', client: list() }, { localAccountId: 'B@h', client: list() }],
+      'B@h',
+    );
+
+    expect(useCalendarStore.getState().selectedCalendarIds).toEqual(['B@h::b', 'B@h::ca:b']);
+  });
+});
diff --git a/stores/calendar-store.ts b/stores/calendar-store.ts
index 5b5acb9f4..55af17e00 100644
--- a/stores/calendar-store.ts
+++ b/stores/calendar-store.ts
@@ -487,12 +487,15 @@ async function refetchAfterOccurrenceMutation(): Promise<void> {
  * calendar is the same. Remap by raw identity so the selection survives instead
  * of silently resetting to "all". Keeps BIRTHDAY_CALENDAR_ID and ids starting
  * with one of `unloadedPrefixes` (calendars of an account that failed to load
- * are unknown, not deleted); drops ids that resolve to no calendar.
+ * are unknown, not deleted); drops ids that resolve to no calendar. A raw id
+ * names a calendar of `rawOwner` (the login a single-account load was for)
+ * when it has one: raw ids repeat across accounts.
  */
 export function reconcileSelectedIds(
   selectedCalendarIds: string[],
   calendars: Calendar[],
   unloadedPrefixes: string[] = [],
+  rawOwner?: string,
 ): string[] {
   const byStoreId = new Set(calendars.map((c) => c.id));
   const rawToStoreId = new Map<string, string>();
@@ -507,6 +510,9 @@ export function reconcileSelectedIds(
     if (id === BIRTHDAY_CALENDAR_ID || byStoreId.has(id)) mapped = id;
     // Before the raw remap: another account may hold the same raw id.
     else if (unloadedPrefixes.some((prefix) => id.startsWith(prefix))) mapped = id;
+    else if (rawOwner && !id.includes(CROSS_ACCOUNT_ID_DELIMITER) && byStoreId.has(buildCrossAccountIdPrefix(rawOwner) + id)) {
+      mapped = buildCrossAccountIdPrefix(rawOwner) + id;
+    }
     else mapped = rawToStoreId.get(rawIdentityOf(id));
     if (mapped && !seen.has(mapped)) {
       out.push(mapped);
@@ -527,8 +533,9 @@ function selectionAfterFetch(
   calendars: Calendar[],
   defaultSelected: string[],
   unloadedPrefixes?: string[],
+  rawOwner?: string,
 ): string[] {
-  const reconciled = reconcileSelectedIds(selectedCalendarIds, calendars, unloadedPrefixes);
+  const reconciled = reconcileSelectedIds(selectedCalendarIds, calendars, unloadedPrefixes, rawOwner);
   if (reconciled.some((id) => id !== BIRTHDAY_CALENDAR_ID)) return reconciled;
   return reconciled.includes(BIRTHDAY_CALENDAR_ID) ? [...defaultSelected, BIRTHDAY_CALENDAR_ID] : defaultSelected;
 }
@@ -785,7 +792,8 @@ interface CalendarStore {
   setSupported: (supported: boolean) => void;
   fetchCalendars: (client: IJMAPClient) => Promise<void>;
   fetchEvents: (client: IJMAPClient, start: string, end: string, options?: FetchEventsOptions) => Promise<void>;
-  fetchAllAccountsCalendars: (accounts: CalendarAccountClient[]) => Promise<void>;
+  /** `activeLocalAccountId`: the login whose calendars un-namespaced selected ids name. */
+  fetchAllAccountsCalendars: (accounts: CalendarAccountClient[], activeLocalAccountId?: string | null) => Promise<void>;
   fetchAllAccountsEvents: (accounts: CalendarAccountClient[], start: string, end: string, options?: FetchEventsOptions) => Promise<void>;
   createEvent: (client: IJMAPClient, event: Partial<CalendarEvent>, sendSchedulingMessages?: boolean) => Promise<CalendarEvent | null>;
   updateEvent: (
@@ -975,7 +983,7 @@ export const useCalendarStore = create<CalendarStore>()(
         }
       },
 
-      fetchAllAccountsCalendars: async (accounts) => {
+      fetchAllAccountsCalendars: async (accounts, activeLocalAccountId) => {
         const epoch = currentStoreEpoch();
         set({ isLoading: true, error: null });
         try {
@@ -1005,6 +1013,7 @@ export const useCalendarStore = create<CalendarStore>()(
               calendars,
               calendars.map(c => c.id),
               unloadedPrefixes,
+              activeLocalAccountId ?? undefined,
             ),
           });
         } catch (error) {