I found a bug for the latest version of bbPress.

If you delete a topic, tags for that topic still remains in the hot tags list.

[@fel64 Member 16 years, 11 months ago]

Is the tag count adjusted? If you have less active tags than tags shown in the hot tags list, tags with 0 topics will be shown. (Not that it isn’t a bug.) Take it to https://trac.bbpress.org/.

[@finalwebsites Participant 16 years, 11 months ago]

actually you didn’t delete the post/thread, but you’re right favorites are also not removed if your remove a thread