[_ck_]

Found my fix after some digging.

edit forum.php

see where this part is near the top

</table>

<?php endif; ?>

<?php if ( $topics || $stickies ) : ?>

change it to this:

</table>

<? global $forum; $forum = get_forum( $forum_id );    // fix for 0.8.2.1 sub-forum bug ?>

<?php endif; ?>

<?php if ( $topics || $stickies ) : ?>

it’s related to this bug which is fixed in the trunk (supposedly)

https://trac.bbpress.org/ticket/704