Cool, found and fixed. As dotagious had narrowed down earlier it is in newthread.php. When you're adding in the sections in there, instead of replacing the whole area, just add the small query to the bottom. The original query is still the same... I. E....
PHP Code:
$DB_site->query("INSERT INTO post (postid,threadid,title,username,userid,dateline,attachmentid,pagetext,allowsmilie,showsignature,ipaddress,iconid,visible,isnews) VALUES (NULL,'$threadid','".addslashes(htmlspecialchars($subject))."','".addslashes($postusername)."','$bbuserinfo[userid]','".time()."','$attachmentid','".addslashes($message)."','$allowsmilie','$signature','$ipaddress','$iconid','1','Y')");
$postid=$DB_site->insert_id();
^^^^ Keep this, with whatever modifications you have done to make your portal software work.
Instead, just add this additional part (from Thread Preview) below it...
PHP Code:
$DB_site->query("UPDATE thread SET firstpostid = '$postid' WHERE threadid = '$threadid'");
I don't have vB Portal installed to test it, but I am pretty sure this would fix the problem with that as well since they are built simillar at this point.