Button replacement disappears on error

If you create a node type that uses attachments, and attach a file you get the remove/keep show/hide button replacement as expected. If you save the node without filling title (or some other form error) when the page reloads the replacement buttons do not appear.

This is caused by Drupal using the cached form to display the form and errors, and not going through hook_form_alter() which loads up the JS code. This happens with other Javascript as well - any module which loads JS files or CSS files in hook_form_alter() will fail to reload them if there's an error on a cached form.