symfony 2 - 对象创建两次

In my current symfony project i work with doctrine.

in one of my controllers i am creating an object and saving it to the db:

$article = new Article();
$article->setName('article');

$em = $this->getDoctrine()->getManager();
$em->persist($article);
$em->flush();

$data = $this->prepareIndexAction();

$html = $this->container->get('templating')->render(
    'index.html.twig',
    ['data' => $data]
);

return new Response($html);

This object is saved two times to the database.

Anybody knows how to deal with this?

Greetings and thanks!