Can't add new user from administration

The latest cvs version does not allow admins to add new users, it always shows the users list.
I got it work by setting the empty $op to arg(3) in the user_admin() function:

function user_admin() {
  $edit = isset($_POST['edit']) ? $_POST['edit'] : '';
  $op = isset($_POST['op']) ? $_POST['op'] : '';

  if (empty($op)) {
    $op = arg(3);
  }
.................