diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 45b2bcd59..8235440f2 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -13350,8 +13350,11 @@ paths:
       tags:
         - MeasurementReminders
       summary: Edit a Vorsorge reminder (v1.17.1)
-      description: Partial edit; omitted fields are left untouched. nextDueAt is recomputed server-side after the cadence
-        merge. Owner-scoped.
+      description: Partial edit; omitted fields are left untouched. nextDueAt is recomputed server-side only when the edit
+        changes when the reminder recurs (intervalDays, rrule, anchorDate compared by value, or enabled switched back
+        on); that recompute also clears a snooze. A notifyHour-only edit keeps the due day and moves the hour on it. Any
+        other edit (label, location, measurementType) leaves nextDueAt as it is, so an open, overdue check-up stays due.
+        Owner-scoped.
       parameters:
         - in: path
           name: id
@@ -26953,7 +26956,7 @@ components:
         enabled:
           type: boolean
       description: Partial edit of a Vorsorge reminder. Omitted fields are left untouched; nextDueAt is recomputed server-side
-        after the patch applies.
+        when the cadence changes and otherwise kept (a notifyHour edit moves only the hour on the same due day).
     MeasurementReminderSnooze:
       type: object
       properties:
diff --git a/src/app/api/measurement-reminders/[id]/__tests__/route.test.ts b/src/app/api/measurement-reminders/[id]/__tests__/route.test.ts
index 97c9fb415..8ca59d072 100644
--- a/src/app/api/measurement-reminders/[id]/__tests__/route.test.ts
+++ b/src/app/api/measurement-reminders/[id]/__tests__/route.test.ts
@@ -231,6 +231,55 @@ describe("PATCH /api/measurement-reminders/[id] — nextDueAt honours explicit-n
     expect("rrule" in persisted).toBe(false);
     expect("anchorDate" in persisted).toBe(false);
 
+    // v1.39.2 — and nextDueAt is not written either. It used to be
+    // recomputed on every PATCH, so correcting the label of an open,
+    // overdue check-up (BASE_ROW is due 2026-01-31, NOW is June) quietly
+    // moved it to its next slot, the same "reminded and gone" defect the
+    // reminder tick had. Only a change to when it recurs reschedules it.
+    expect("nextDueAt" in persisted).toBe(false);
+    expect("snoozedUntil" in persisted).toBe(false);
+  });
+
+  it("an edit that resends the unchanged cadence keeps an overdue slot", async () => {
+    findFirstMock.mockResolvedValue(BASE_ROW);
+
+    const res = await PATCH(
+      makeRequest({ label: "New label", intervalDays: 30, rrule: null }),
+      params,
+    );
+    expect(res.status).toBe(200);
+
+    const persisted = updateMock.mock.calls[0]?.[0]?.data as Record<
+      string,
+      unknown
+    >;
+    expect("nextDueAt" in persisted).toBe(false);
+  });
+
+  it("a notify-hour edit keeps the due day and moves only the hour", async () => {
+    findFirstMock.mockResolvedValue(BASE_ROW);
+
+    const res = await PATCH(makeRequest({ notifyHour: 18 }), params);
+    expect(res.status).toBe(200);
+
+    const persisted = updateMock.mock.calls[0]?.[0]?.data as Record<
+      string,
+      unknown
+    >;
+    // 2026-01-31 18:00 in Berlin (UTC+1 in winter).
+    expect(persisted.nextDueAt).toEqual(new Date("2026-01-31T17:00:00Z"));
+  });
+
+  it("re-enabling a disabled reminder schedules it from now", async () => {
+    findFirstMock.mockResolvedValue({ ...BASE_ROW, enabled: false });
+
+    const res = await PATCH(makeRequest({ enabled: true }), params);
+    expect(res.status).toBe(200);
+
+    const persisted = updateMock.mock.calls[0]?.[0]?.data as Record<
+      string,
+      unknown
+    >;
     const expected = computeReminderNextDueAt(BASE_ROW, TZ, NOW);
     expect(persisted.nextDueAt).toEqual(expected);
   });
diff --git a/src/app/api/measurement-reminders/[id]/route.ts b/src/app/api/measurement-reminders/[id]/route.ts
index f51d742ca..082d4cf50 100644
--- a/src/app/api/measurement-reminders/[id]/route.ts
+++ b/src/app/api/measurement-reminders/[id]/route.ts
@@ -1,8 +1,10 @@
 /**
  * v1.17.1 — Vorsorge (measurement) reminder by id: get + patch + delete.
  *
- * PATCH re-derives the server-authoritative `nextDueAt` after applying
- * the (mutually-exclusive cadence) edit. DELETE removes the row; the
+ * PATCH re-derives the server-authoritative `nextDueAt` when the edit
+ * changes when the reminder recurs (interval, rule, anchor, or re-enabling
+ * it); a notify-hour edit moves the hour on the same due day, and any other
+ * edit leaves the due date alone. DELETE removes the row; the
  * confirmation dialog says the reminder is permanently deleted, and nothing
  * here needs a tombstone to keep that promise honest.
  */
@@ -30,6 +32,7 @@ import {
   type ReminderScheduleInput,
 } from "@/lib/measurement-reminders/scheduling";
 import { toMeasurementReminderDto } from "@/lib/measurement-reminders/dto";
+import { wallClockInTz, zonedWallClockToUtc } from "@/lib/tz/wall-clock";
 
 type RouteParams = { params: Promise<{ id: string }> };
 
@@ -184,14 +187,50 @@ export const PATCH = apiHandler(
       // (Coach-suggested) cadence keeps self-expiring.
       endsOn: existing.endsOn,
     };
-    const after =
-      existing.lastSatisfiedAt && existing.lastSatisfiedAt > now
-        ? existing.lastSatisfiedAt
-        : now;
-    updateData.nextDueAt = computeReminderNextDueAt(merged, timezone, after);
-    // v1.37.20 (#223) — a cadence edit recomputes `nextDueAt`, so it clears
-    // the snooze cursor: the cycle the snooze pushed back no longer exists.
-    updateData.snoozedUntil = null;
+    // v1.39.2 — only an edit to WHEN the reminder recurs reschedules it. A
+    // label, location or type edit used to recompute too, and since the
+    // recompute searches strictly after now, correcting the label of an
+    // open, overdue check-up quietly moved it to its next slot. Compared by
+    // value, because the edit forms resend every field on each save.
+    const sameInstant = (a: Date | null, b: Date | null) =>
+      (a?.getTime() ?? null) === (b?.getTime() ?? null);
+    const cadenceChanged =
+      merged.intervalDays !== existing.intervalDays ||
+      merged.rrule !== existing.rrule ||
+      !sameInstant(merged.anchorDate, existing.anchorDate) ||
+      (updateData.enabled === true && !existing.enabled);
+    if (cadenceChanged) {
+      const after =
+        existing.lastSatisfiedAt && existing.lastSatisfiedAt > now
+          ? existing.lastSatisfiedAt
+          : now;
+      updateData.nextDueAt = computeReminderNextDueAt(merged, timezone, after);
+      // v1.37.20 (#223) — a cadence edit recomputes `nextDueAt`, so it clears
+      // the snooze cursor: the cycle the snooze pushed back no longer exists.
+      updateData.snoozedUntil = null;
+    } else if (
+      merged.notifyHour !== existing.notifyHour &&
+      existing.nextDueAt !== null
+    ) {
+      // A new notify hour keeps the due DAY and moves the hour on it, so an
+      // open slot stays open. A snooze pinned to that same slot moves with it.
+      const day = wallClockInTz(existing.nextDueAt, timezone);
+      const moved = zonedWallClockToUtc(
+        {
+          year: day.year,
+          month: day.month,
+          day: day.day,
+          hour: merged.notifyHour,
+          minute: 0,
+          second: 0,
+        },
+        timezone,
+      );
+      updateData.nextDueAt = moved;
+      if (sameInstant(existing.snoozedUntil, existing.nextDueAt)) {
+        updateData.snoozedUntil = moved;
+      }
+    }
 
     const updated = await prisma.measurementReminder.update({
       where: { id },
diff --git a/src/lib/openapi/routes/measurement-reminders.ts b/src/lib/openapi/routes/measurement-reminders.ts
index 8fdbf8742..3312ad0b7 100644
--- a/src/lib/openapi/routes/measurement-reminders.ts
+++ b/src/lib/openapi/routes/measurement-reminders.ts
@@ -115,7 +115,7 @@ export const measurementReminderPaths: NonNullable<ZodOpenApiObject["paths"]> =
         tags: ["MeasurementReminders"],
         summary: "Edit a Vorsorge reminder (v1.17.1)",
         description:
-          "Partial edit; omitted fields are left untouched. nextDueAt is recomputed server-side after the cadence merge. Owner-scoped.",
+          "Partial edit; omitted fields are left untouched. nextDueAt is recomputed server-side only when the edit changes when the reminder recurs (intervalDays, rrule, anchorDate compared by value, or enabled switched back on); that recompute also clears a snooze. A notifyHour-only edit keeps the due day and moves the hour on it. Any other edit (label, location, measurementType) leaves nextDueAt as it is, so an open, overdue check-up stays due. Owner-scoped.",
         requestParams: { path: z.object({ id: z.string() }) },
         requestBody: {
           required: true,
diff --git a/src/lib/validations/measurement-reminders.ts b/src/lib/validations/measurement-reminders.ts
index 31e9d2f6a..724e2b2d4 100644
--- a/src/lib/validations/measurement-reminders.ts
+++ b/src/lib/validations/measurement-reminders.ts
@@ -185,7 +185,7 @@ export const updateMeasurementReminderSchema = z
   .meta({
     id: "MeasurementReminderUpdate",
     description:
-      "Partial edit of a Vorsorge reminder. Omitted fields are left untouched; nextDueAt is recomputed server-side after the patch applies.",
+      "Partial edit of a Vorsorge reminder. Omitted fields are left untouched; nextDueAt is recomputed server-side when the cadence changes and otherwise kept (a notifyHour edit moves only the hour on the same due day).",
   });
 
 export type UpdateMeasurementReminderInput = z.infer<