Click on marker clones other input

Some news.
The problem is my custom module that use a simple form_alter to "transform" a submit button to an image.
Here is the code:

function alterator_form_alter(&$form, &$form_state, $form_id) {
  if ($form['#id'] == 'user-login-form') {
    $form['actions']['submit']['#type'] = 'image_button';
    $form['actions']['submit']['#title'] = t('Login');
    $form['actions']['submit']['#src'] = drupal_get_path('theme', 'mytheme') . '/images/login.png';
  }
}

This code is correct, the function works, but *every* form that I edit with this hook has this beahviour (the "clone" of input fields.

Another update: it seems a conflict with Hint module.
See http://drupal.org/node/1995664