Chyba ve startovani session v 2.1 RC3

Updatoval jsem muj projekt z 2.1 RC1 (vse fungovalo) na RC3 a hlasi mi to chybu:

Possible problem: you are starting session while already having some data in output buffer. This may not work if the outputted data grows. Try starting the session earlier.

public function initialize()
        {
            date_default_timezone_set('Europe/Prague');
            Nette\Caching\Storages\FileStorage::$useDirectories = TRUE;
            $this->getByType("Nette\Http\Session")->start(); //tady se to zastavi
            header('X-Frame-Options: SAMEORIGIN');
            @header('X-Powered-By: Nette Framework');
            @header('Content-Type: text/html; charset=utf-8');
            Nette\Utils\SafeStream::register();

Stejne chovani i na sandboxu a i pri nastaveni nette: session: autoStart: true

PHP verze 5.4.19.