route: notFound, setting params error

i Have in my route conf:

    $router->notFound(array(
    'module' => 'public',
    'controller' => 'error',
    'action' => 'index',
    'params' => '404'
));

in controller:

    public function indexAction($error = NULL) {
    var_dump($error);
    die();
    }

the response is: string(2) "04", i need 404 param

but if change the route to:

      $router->notFound(array(
    'module' => 'public',
    'controller' => 'error',
    'action' => 'index',
    'params' => '0404'
    ));

the response is: string(2) "404" , and it oks for me!..

and i need that 404 param... why is this problem??, bug in notFound?