diff --git a/src/components/settings/access/__tests__/managed-profile-edit-patch.test.ts b/src/components/settings/access/__tests__/managed-profile-edit-patch.test.ts
new file mode 100644
index 000000000..2de25b373
--- /dev/null
+++ b/src/components/settings/access/__tests__/managed-profile-edit-patch.test.ts
@@ -0,0 +1,68 @@
+/**
+ * What the managed-record edit form sends, and what it must not.
+ *
+ * The route reads an absent key as "leave it", so the diff this function
+ * computes is the whole of the promise that a save touches only what somebody
+ * moved. The case worth pinning is the language: a record with none opens its
+ * control on the ACTOR's, so comparing the control against the record's column
+ * made every save of such a record carry `locale` — and a guardian who only
+ * corrected the timezone wrote their own language into somebody else's record.
+ */
+import { describe, expect, it } from "vitest";
+
+import { managedProfileEditPatch } from "@/components/settings/access/managed-profile-edit-form";
+import type { ManagedProfileView } from "@/lib/queries/use-managed-profiles";
+
+const record: ManagedProfileView = {
+  id: "rec_1",
+  displayName: "Managed record",
+  dateOfBirth: null,
+  gender: null,
+  locale: null,
+  timezone: "Europe/Berlin",
+  recordKind: "managed",
+};
+
+const draft = {
+  displayName: "Managed record",
+  dateOfBirth: "",
+  locale: "en" as const,
+  gender: null,
+  timezone: "Europe/Berlin",
+};
+
+describe("managedProfileEditPatch", () => {
+  it("leaves the language out when a record with none only moves its timezone", () => {
+    const patch = managedProfileEditPatch(
+      record,
+      { ...draft, timezone: "Europe/Madrid" },
+      "en",
+    );
+
+    expect(patch).toEqual({ timezone: "Europe/Madrid" });
+  });
+
+  it("answers null when a record with no language is not touched at all", () => {
+    expect(managedProfileEditPatch(record, draft, "en")).toBeNull();
+  });
+
+  it("sends the language once somebody picks a different one", () => {
+    const patch = managedProfileEditPatch(
+      record,
+      { ...draft, locale: "de" },
+      "en",
+    );
+
+    expect(patch).toEqual({ locale: "de" });
+  });
+
+  it("sends the language when a record that has one is moved off it", () => {
+    const patch = managedProfileEditPatch(
+      { ...record, locale: "de" },
+      { ...draft, locale: "en" },
+      "de",
+    );
+
+    expect(patch).toEqual({ locale: "en" });
+  });
+});
diff --git a/src/components/settings/access/managed-profile-edit-form.tsx b/src/components/settings/access/managed-profile-edit-form.tsx
index 44a0f4ba7..5d287647d 100644
--- a/src/components/settings/access/managed-profile-edit-form.tsx
+++ b/src/components/settings/access/managed-profile-edit-form.tsx
@@ -131,10 +131,12 @@ function ManagedProfileEditFields({
   // A record with no recorded language opens on the actor's, which is the same
   // default the creation form uses. It is a starting point for a control the
   // person is looking at, not an inference written behind their back — nothing
-  // is sent until they save.
-  const [locale, setLocale] = useState<Locale>(
+  // is sent unless they move it, which is why the seed is frozen at mount and
+  // handed to the patch builder as what "moved" is measured against.
+  const [seededLocale] = useState<Locale>(() =>
     isLocale(profile.locale) ? profile.locale : actorLocale,
   );
+  const [locale, setLocale] = useState<Locale>(seededLocale);
   const [gender, setGender] = useState<ManagedProfileGender>(profile.gender);
   const [timezone, setTimezone] = useState(profile.timezone);
   const [error, setError] = useState<string | null>(null);
@@ -143,13 +145,17 @@ function ManagedProfileEditFields({
   const timezoneIssue = isValidTimezone(timezone)
     ? null
     : "recordSharing.managed.timezoneInvalid";
-  const patch = managedProfileEditPatch(profile, {
-    displayName,
-    dateOfBirth,
-    locale,
-    gender,
-    timezone,
-  });
+  const patch = managedProfileEditPatch(
+    profile,
+    {
+      displayName,
+      dateOfBirth,
+      locale,
+      gender,
+      timezone,
+    },
+    seededLocale,
+  );
   const blocked =
     nameIssue !== null || timezoneIssue !== null || patch === null;
 
@@ -333,13 +339,22 @@ interface ManagedProfileEditDraft {
 export function managedProfileEditPatch(
   profile: ManagedProfileView,
   draft: ManagedProfileEditDraft,
+  /**
+   * The language the control opened on, which is the record's own or — for a
+   * record that has none — the actor's. Compared against instead of
+   * `profile.locale` because those two differ exactly when the record has no
+   * language: comparing against the column made every save of a record like
+   * that carry `locale`, so moving only the timezone wrote the actor's
+   * language into somebody else's record.
+   */
+  seededLocale: Locale,
 ): Omit<UpdateManagedProfileInput, "profileId"> | null {
   const displayName = draft.displayName.trim();
   const dateOfBirth = draft.dateOfBirth.length > 0 ? draft.dateOfBirth : null;
   const patch: Omit<UpdateManagedProfileInput, "profileId"> = {
     ...(displayName !== (profile.displayName ?? "") ? { displayName } : {}),
     ...(dateOfBirth !== profile.dateOfBirth ? { dateOfBirth } : {}),
-    ...(draft.locale !== profile.locale ? { locale: draft.locale } : {}),
+    ...(draft.locale !== seededLocale ? { locale: draft.locale } : {}),
     ...(draft.gender !== profile.gender ? { gender: draft.gender } : {}),
     ...(draft.timezone !== profile.timezone
       ? { timezone: draft.timezone }