Warning message (warning: uksort(): Array was modified...)

Here's the code:

function theme_role_weights_admin_new_role($form) {
  $header = array(t('Name'), array('data' => t('Operations'), 'colspan' => 2));

  $user_roles = user_roles();
  if (variable_get('role_weights_reorder_forms', FALSE)) {
    uksort($user_roles, '_role_weights_rid_compare');
  }

  foreach ($user_roles as $rid => $name) {
    $edit_permissions = l(t('edit permissions'), 'admin/user/permissions/'. $rid);

    // Drupal core redirects if the rid is DRUPAL_ANONYMOUS_RID or DRUPAL_AUTHENTICATED_RID.
    // We prevent this by shifting the rid.
    _role_weights_shift_rid($rid);
    $rows[] = array($name, l(t('edit role'), 'admin/user/roles/edit/'. $rid), $edit_permissions);
  }
  $rows[] = array(drupal_render($form['name']), array('data' => drupal_render($form['submit']), colspan => 2));

  return drupal_render($form) . theme('table', $header, $rows);
}