Why submission result doesn't update?

import { action, useSubmission } from "@solidjs/router";
import { Show } from "solid-js";

const addPost = action(async (formData: FormData) => {
  const title = formData.get("title") as string;
  if (!title || title.length < 4) {
    return {
      isError: true,
      error: "Title must be at least 4 characters",
    };
  }
  console.log("Post added: ", { title });
}, "addPost");

export default function Page() {
  const submission = useSubmission(addPost);
  return (
    <form action={addPost} method="post">
      <input name="title" />
      <Show when={submission.result?.isError}>
        <p>{submission.result?.error}</p>
      </Show>
      <button>Submit</button>
    </form>
  );
}

{
  isError: true,
  error: "Title must be at least 4 characters",
}