Не держатся отметки "новые сообщения" до их прочте

//
// Handle marking posts
//
if ( $mark_read == 'topics' )
{
      // Begin Simple Subforums MOD
   $mark_list = ( isset($HTTP_GET_VARS['mark_list']) ) ? explode(',', $HTTP_GET_VARS['mark_list']) : array($forum_id);
   $old_forum_id = $forum_id;
   // End Simple Subforums MOD
if ( $userdata['session_logged_in'] )
   {
      $sql = "SELECT MAX(post_time) AS last_post
         FROM " . POSTS_TABLE . "
         WHERE forum_id = $forum_id";
      if ( !($result = $db->sql_query($sql)) )
      {
         message_die(GENERAL_ERROR, 'Could not obtain forums information', '', __LINE__, __FILE__, $sql);
      }

      if ( $row = $db->sql_fetchrow($result) )
      {
         $tracking_forums = ( isset($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_f']) ) ? unserialize($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_f']) : array();
         $tracking_topics = ( isset($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_t']) ) ? unserialize($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_t']) : array();

         if ( ( count($tracking_forums) + count($tracking_topics) ) >= 150 && empty($tracking_forums[$forum_id]) )
         {
            asort($tracking_forums);
            unset($tracking_forums[key($tracking_forums)]);
         }

         if ( $row['last_post'] > $userdata['user_lastvisit'] )
         {
            $tracking_forums[$forum_id] = time();            
            // Begin Simple Subforums MOD
            $set_cookie = true;
            if( isset($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_f']) )
            {
               $HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_f'] = serialize($tracking_forums);
            }
            // End Simple Subforums MOD

         }
      }
      // Begin Simple Subforums MOD
      if( $set_cookie )
      {
         setcookie($board_config['cookie_name'] . '_f', serialize($tracking_forums), 0, $board_config['cookie_path'], $board_config['cookie_domain'], $board_config['cookie_secure']);
      }
      $forum_id = $old_forum_id;
      // End Simple Subforums MOD


      $template->assign_vars(array(
         'META' => '<meta>')
      );
   }

   $message = $lang['Topics_marked_read'] . '<br><br>' . sprintf($lang['Click_return_forum'], '<a>', '</a> ');
   message_die(GENERAL_MESSAGE, $message);
}
//
// End handle marking posts
//

$tracking_topics = ( isset($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_t']) ) ? unserialize($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_t']) : '';
$tracking_forums = ( isset($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_f']) ) ? unserialize($HTTP_COOKIE_VARS[$board_config['cookie_name'] . '_f']) : '';