doctrine bug

$qb = $em->createQueryBuilder()
    ->select('t, c, p')
    ->from('Task', 't')
    ->leftJoin('t.children', 'c')
    ->leftJoin('t.parent', 'p')
    ->orderBy('t.root, t.lft')
;

foreach( $qb->getQuery()->getResult() as $task)
{
    $task->getChildren()->count();
}