On account creation, the message is not displayed
A workaround would be to manually create message in hook_user_insert, with code like:

function mymodule_user_insert(&amp;$edit, $account, $category) {
  drupal_set_message(t('Account created, wait for approval.'), 'status');
}


Alternative place is hook_entity_insert:

function mymodule_entity_insert($entity, $type) {
  if ($type == 'user') {
    drupal_set_message(t('Account created, wait for approval.'), 'status');
  }
}


Problem is - it is possible that the same error will hide this one too. Benefit: it's easier to experiment with small custom hook, than to debug core.