Module 'stumble' can not be uninstalled

Hi,

when trying to uninstall the 'Stumble' module, I'm getting:

Fatal error: Call to undefined function stumble_variables() in /var/www/drupal/sites/all/modules/stumble/stumble.install on line 13

The function around line 13 reads:

/**
 * Implementation of hook_uninstall().
 */
function stumble_uninstall() {
  $variables = array_keys(stumble_variables());
  foreach ($variables as $variable) {
    variable_del($variable);
  }
}

The module remains and can not be uninstalled. Also, this is reproducable in 5 of 5 D5 sites (al I had this module installed). Thus setting this to 'critical'.

Thanks & greetings, -asb