Open admin/forum.php and find
PHP Code:
$DB_site->query("UPDATE forum
SET
styleid='$styleset', title='".addslashes($title)."', description='".addslashes($description)."',
active='$isactive', displayorder='$displayorder', parentid='$parentid', parentlist=$parentlist,
allowposting='$allowposting', cancontainthreads='$cancontainthreads', daysprune='$daysprune',
newpostemail='".addslashes($newpostemail)."', newthreademail='".addslashes($newthreademail)."',
moderatenew='$moderatenew', allowhtml='$aallowhtmlcode', allowbbcode='$aallowbbcode',
allowimages='$aallowimgcode', allowsmilies='$aallowsmilies', allowicons='$aallowicons',
styleoverride='$styleoverride', allowratings='$allowratings', countposts='$countposts',
moderateattach='$moderateattach', storereply='$storereply', storethread='$storethread', minpostsperday='$minpostsperday'
WHERE forumid='$forumid'");
Below, add
PHP Code:
$DB_site->query("UPDATE forum SET styleid='$styleset', styleoverride='$styleoverride' WHERE parentid = '$forumid'");
Should work.