wrong 'You can only edit reservations which are unconfirmed.' in merci_form

in merci_form function (merci.module)

if ($node->merci['status'] != MERCI_STATUS_UNCONFIRMED && !user_access('create confirmed reservations')&& !user_access('manage MERCI') && !user_access('administer MERCI') && !user_access('create confirmed reservations')) {
    form_set_error('merci_status', t('You can only edit reservations which are unconfirmed.'));
    drupal_access_denied();
  }

The $node->merci['status'] is not set after preview or validation error. But $node->merci_status is.

And above this code, a variable $merci_status_default is assigned to $node->merci_status if set or to $node->merci['status'] (which is set when the form is called for the first time).

Directly using $merci_status_default fixes the problem.