ArrayHydrator with composite primary key

$query = $em->createQuery("SELECT c,d FROM ResourceClosure c JOIN c.descendant d WHERE c.ancestor = 1");

echo 'ObjectHydrator result count = '.count($query->getResult()).PHP_EOL;
echo 'ArrayHydrator result count = '.count($query->getArrayResult()).PHP_EOL;

ObjectHydrator result count = 2 
ArrayHydrator result count = 1 

/**
 * @Entity
 */
class ResourceClosure
{
    /**
     * @Id
     * @ManyToOne(targetEntity="Resource")
     * @JoinColumn(name="ancestor_id", referencedColumnName="id")
     *
     */
    private $ancestor;

    /**
     * @Id
     * @ManyToOne(targetEntity="Resource")
     * @JoinColumn(name="descendant_id", referencedColumnName="id")
     * @var Resource
     */
    private $descendant;

    /**
     * @Column(name="depth", type="integer")
     * @var integer
     */
    private $depth;
}

$resource1 = new Entity\Resource('resource1');
$em->persist($resource1);

$resource2 = new Entity\Resource('resource2');
$em->persist($resource2);

$em->flush();

$closure1 = new Entity\ResourceClosure();
$closure1->setAncestor($resource1)
                ->setDescendant($resource1)
                ->setDepth(0);

$em->persist($closure1);


$closure2= new Entity\ResourceClosure();
$closure2->setAncestor($resource1)
                ->setDescendant($resource2)
                ->setDepth(1);

$em->persist($closure2);


$em->flush();