Users can register despite capacity reaching limit

in registration_form_validate(), the check for whether capacity has been reached does not prevent the user from creating a registration if the host entity is already full.

  if (!registration_has_room($registration->entity_type, $registration->entity_id, $count)) {
    drupal_set_message(t('Sorry, there are insufficient slots remaining for this event.'));
  }

to

  if (!registration_has_room($registration->entity_type, $registration->entity_id, $count)) {
    form_set_error('', t('Sorry, there are insufficient slots remaining for this event.'));
  }