Order by meta_key where value is serialized

I’d order post by meta_key but i’ve a problem with meta_value because is serialized object.

a:2:{s:5:"count";d:9750;s:7:"timeout";i:1358466733;}

I’d order my post per count value.

I use below code but order correctly until wp version 3.4.2 after update to 3.5 order by date:

if (have_posts()) :
    $args=array(
    'meta_key' => 'tweets_count',
    'orderby' => 'meta_value',
    'showposts' => 10,
      );
      query_posts($args);
      while (have_posts()) : the_post();
//loop

Help me please.