Custom roles missing from post author dropdown

// Filter to fix the Post Author Dropdown
add_filter('wp_dropdown_users', 'theme_post_author_override');
function theme_post_author_override($output)
{
    global $post, $user_ID;

  // return if this isn't the theme author override dropdown
  if (!preg_match('/post_author_override/', $output)) return $output;

  // return if we've already replaced the list (end recursion)
  if (preg_match ('/post_author_override_replaced/', $output)) return $output;

  // replacement call to wp_dropdown_users
    $output = wp_dropdown_users(array(
      'echo' => 0,
        'name' => 'post_author_override_replaced',
        'selected' => empty($post->ID) ? $user_ID : $post->post_author,
        'include_selected' => true
    ));

    // put the original name back
    $output = preg_replace('/post_author_override_replaced/', 'post_author_override', $output);

  return $output;
}