content types appearing twice in dropdown

The list of content types to add at user/UID/notifications/group has each content type twice:

The mistake is here, but I'm not sure what is meant to be happening with the first $content_types:

function og_notifications_add_form($form_state, $account) {
  $content_types = array_filter(variable_get('og_notifications_content_types', array()));
  $content_names = node_get_types('names');
  foreach ($content_types as $type) {
    $content_types[$type] = $content_names[$type];
  }