Can not save the access restricted gmapfield

If the edit rights of gmapfield is access restricted by hook_field_access(), then the validate callback always set this error: "Please enter a valid GMap macro."
The field is not required.
Maybe the solution is (line 736):

function _gmapfield_validate(&$item, $delta, $field, $node) {
  // Check for valid GMap Macro
  if (!gmapfield_content_is_empty($item, $field) AND !_gmapfield_validate_macro($item['gmap_macro'])) {
    form_set_error($field['field_name'] .']['. $delta. '][title', t('Please enter a valid GMap macro.'));
  }
  return TRUE;
}