'#validate' does not work in sub-forms

I create an Ubercart settings form for the PayJunction processing gateway.

The form includes a login & password, which works great now, but I needed to set the password to a default on validation if the user did not change the password content (otherwise it gets erased!)

function _mo_payjunction_settings_form() {
  // add login/password items
  ...
  // password requires a validation
  $form['#validate'][] = 'mo_payjunction_validate';
  ...
  return $form;
}

This does not work because you "improperly" merge the array as shown here:

  ...
      if (function_exists($gateway['settings'])) {
        $gateway_settings = $gateway['settings']();
        if (is_array($gateway_settings)) {
          $form['gateways'][$gateway['id']] = array_merge($form['gateways'][$gateway['id']], $gateway_settings);
        }
      }
  ...

Of course, using array_merge() is real fast, but it should never be that large an array and it is only for admins. So I think we could have yet another foreach() that checks the $gateway_settings and for any #<name> we put that at the top of the destination array. That way #validate and #submit (at least) would work.

This is very minor since there is an okay work around which is to have a hook_form_alter() which can check for the uc_payment_gateways_form and adds the necessary validation function(s), but that's a bit ugly.

Thank you.
Alexis Wilke