diff --git a/web/src/pages/admin/autoscan/sourceForm.test.ts b/web/src/pages/admin/autoscan/sourceForm.test.ts
index 4eba5046e8..45db57e253 100644
--- a/web/src/pages/admin/autoscan/sourceForm.test.ts
+++ b/web/src/pages/admin/autoscan/sourceForm.test.ts
@@ -38,6 +38,7 @@ describe("editedSourceBody", () => {
     const source = pollSource();
     const draft = {
       ...draftFromSource(source, descriptor),
+      configDirty: true,
       label: "  Basement ",
       intervalStr: "1200",
       mappings: [newMapping("/mnt/media/tv", " /data/tv "), newMapping("", "")],
@@ -67,6 +68,38 @@ describe("editedSourceBody", () => {
     expect(editedSourceBody(source, draft, {}).connection_id).toBeNull();
   });
 
+  it("sends the stored config back when the config was not edited", () => {
+    // Saving rebuilds the config from the form, which fills in declared
+    // defaults. Sending that for a label change would make the server
+    // restart the source's poll marker from now.
+    const source = pollSource();
+    const draft = { ...draftFromSource(source, descriptor), label: "Renamed", intervalStr: "1200" };
+    expect(
+      editedSourceBody(source, draft, { lookback: "24h", window: "7d" }).source_config,
+    ).toEqual(source.source_config);
+  });
+
+  it("still migrates a row holding legacy CephFS keys on its first save", () => {
+    const source = pollSource({
+      plugin_id: "silo.autoscan.cephfs",
+      capability_id: "cephfs",
+      source_config: { tv_nested_paths: "/b" },
+    });
+    const draft = { ...draftFromSource(source, descriptor), label: "Renamed" };
+    expect(editedSourceBody(source, draft, { tv_flat_paths: "/b" }).source_config).toEqual({
+      tv_flat_paths: "/b",
+    });
+  });
+
+  it("counts a webhook provider change as a config edit", () => {
+    const source = webhookSource();
+    const draft = draftFromSource(source, descriptor);
+    draft.sourceConfig = { ...draft.sourceConfig, webhook_provider: "radarr" };
+    expect(editedSourceBody(source, draft, { webhook_provider: "radarr" }).source_config).toEqual({
+      webhook_provider: "radarr",
+    });
+  });
+
   it("round-trips a webhook source unchanged", () => {
     const source = webhookSource();
     const draft = draftFromSource(source, descriptor);
diff --git a/web/src/pages/admin/autoscan/sourceForm.ts b/web/src/pages/admin/autoscan/sourceForm.ts
index af1ce27141..751b193857 100644
--- a/web/src/pages/admin/autoscan/sourceForm.ts
+++ b/web/src/pages/admin/autoscan/sourceForm.ts
@@ -224,6 +224,25 @@ export function draftConnectionId(draft: Pick<SourceDraft, "connectionId">): str
   return draft.connectionId && draft.connectionId !== "__none__" ? draft.connectionId : null;
 }
 
+/**
+ * Whether the save has to send the config built from the form: the schema
+ * form marked the draft dirty, the webhook provider (which has its own
+ * control) differs from the stored one, or the row still holds legacy keys
+ * that its first save migrates forward.
+ */
+function configEdited(source: AutoscanSource, draft: SourceDraft): boolean {
+  if (draft.configDirty) return true;
+  const stored = source.source_config ?? {};
+  if (
+    ownsLegacyAliases(source) &&
+    Object.keys(LEGACY_CONFIG_KEY_ALIASES).some((key) => key in stored)
+  ) {
+    return true;
+  }
+  const chosen = draft.sourceConfig[WEBHOOK_PROVIDER_KEY];
+  return chosen !== undefined && chosen !== stored[WEBHOOK_PROVIDER_KEY];
+}
+
 /**
  * The complete PUT body for an edited source. Every field is sent: the edit
  * dialog owns all of them, and the list's enabled switch owns `enabled`, which
@@ -243,7 +262,13 @@ export function editedSourceBody(
     // rather than clearing it if one slips through.
     poll_interval_seconds: interval.valid ? interval.seconds : source.poll_interval_seconds,
     path_rewrites: usableMappings(draft.mappings),
-    source_config: normalizeSourceConfig(serializedConfig),
+    // A config the operator did not touch goes back exactly as stored.
+    // Rebuilding it fills in defaults and drops keys the descriptor no longer
+    // declares, and the server restarts a poll source from now whenever its
+    // source_config changes.
+    source_config: configEdited(source, draft)
+      ? normalizeSourceConfig(serializedConfig)
+      : { ...(source.source_config ?? {}) },
     label: draft.label.trim(),
   };
 }