Wordpress获取多个类别的帖子

I'm tring to use 'category__and' filter in WP_Query function to get some posts out and I get nothing!

here's my code:

$query_args = array( 'category__and' => array(44,43), 'posts_per_page' => 9, 'no_found_rows' => 1, 'post_status' => 'publish', 'post_type' => 'product');
$r = new WP_Query($query_args);
if ($r->have_posts()) { ............

Important note: I have posts in both categories 44&43. When I remove the 'category__and' I get all posts.