Doctrine thrown exception, when it is trying to remove not initialized proxy.

Introduction:
I have a Product, which has many (OneToMany collection) Pictures. Picture has a File (ManyToOne with cascade=

).
The problem:
When I remove a picture from a product

$product->pictures->removeElement($picture);
$picture->resetProduct();

doctrine removes picture, then cascade removes file, but file is not yet initialized. Doctrine tries to check entity state:

    public function getEntityState($entity, $assume = null)
    {
        $oid = spl_object_hash($entity);
        if ( ! isset($this->_entityStates[$oid])) {
...
            if ($assume === null) {
                if ($this->_em->getClassMetadata(get_class($entity))->getIdentifierValues($entity)) {
                    $this->_entityStates[$oid] = self::STATE_DETACHED;
...

The getIdentifierValues method tries to take entity id through reflection, but id field is absent.
I think that the getEntityState method should support case when entity is instance of IProxy...