Open the topic-tags.php of your theme.
You would find something like this:

<?php if ( $public_tags ) : ?>
<div id="othertags">
		<ul id="yourtaglist">
		<?php foreach ( $public_tags as $tag ) : ?>
			<li id="tag-<?php echo $tag->tag_id; ?>_<?php echo $tag->user_id; ?>">
				<a href="<?php bb_tag_link(); ?>" rel="tag"><?php bb_tag_name(); ?></a> <?php $tags = bb_get_tag_remove_link (); if ($tags) echo '<small>'.$tags.'</small>'; ?>
			</li>
		<?php endforeach; ?>
		</ul>
	</div>

Replace it with:

<?php if ( bb_get_topic_tags() ) : ?>
		<?php bb_list_tags(); ?>

That's it!

You can also view the changes to topic-tags.php of the default theme in the trac:
http://trac.bbpress.org/changeset?old_path=%2Ftrunk%2Fbb-templates%2Fkakumei%2Ftopic-tags.php&old=940&new_path=%2Ftrunk%2Fbb-templates%2Fkakumei%2Ftopic-tags.php&new=2344