Looking at the code, I don't think it would be overridden by the router_listener. The router listener sets the request->attributes but the format_listener uses request->setRequestFormat. The [getter on request](https://github.com/symfony/symfony/blob/master/src/Symfony/Component/HttpFoundation/Request.php#L1297) should still returns the set request format because it only uses the attributes when the format is empty.