memo is rerun but any side effects subscribed are'nt reran

const [jsonData, { mutate: setJsonData }] = createResource(initJsonData);
const [saved, setSaved] = createWritableMemo(
  on(jsonData, () => {
    console.log("update saved");
    return false;
  }),
);

createEffect(() => console.log("json data:", jsonData()));
createEffect(() => console.log("saved:", saved()));