If you look at the forum list, it states that the latest reply was 38 minutes ago:

However, if you click through to the post itself, you can see that the time doesn't match up:

It doesn't, however, seem to be like that for all posts. I presume that forum's updated_at timestamp is being touched any time a comment is added, edited, or a solution marked? Perhaps changing the description in the forum list to 'latest activity' rather than 'latest reply' would clear things up. If so, I'd say this is a trivial matter.