Problem with meta_value order after update

Hi,
i use following array and works fine… sort post by meta_key where value of t_count is a number.

$args = array(
     'posts_per_page' => 10,
     'meta_key' => 't_count',
      'orderby' => 'meta_value',
       );
          query_posts($args);

I use 3.4.2 but if I upgrade to 3.5 array above do not sort correctly.
I’ve try also meta_value_num but do not works fine.
Could you help me?
Thanks