Symfony/Doctrine tries to persist logged in user without a password

Every time I call EntityManager::flush in any controller action to save any object, the ORM magic tries to also persist the user object from the currently logged in user if I had used any kind of Symfony security before. This object does not have any credentials stored because Symfony correctly called User::eraseCredentials. Do I have to remove the User manually from the EntityManager or do I miss some magic property in the Entity?