[Opserty]

Try this in global_start it should work I think:

PHP Code:

if (THIS_SCRIPT == 'showthread')
{
    $thread_description = $db->query_first("SELECT pagetext
        FROM " . TABLE_PREFIX . "post
        WHERE threadid = $threadid
        ORDER BY postid
        ASC
        LIMIT 1");

    $thread_description['pagetext'] = htmlspecialchars_uni($thread_description['pagetext']);
} 


Bearing in mind your running an extra query on every showthread page.