Bug tracker
"Last Post" updated when replying to unapproved topics (duplicate)
Comments / History
I think we implemented a change recently where a reply to an unapproved topic made the topic approved and the first approved message being the start of the topic. I could be wrong here though and the topic is still invisible (then the last post info should not be updated and the topic not reachable and not visible by normal users).
It shouldn't be difficult to fix. Just don't update anything on the forums table if the post is being made to an unapproved topic. Once the topic is approved then go through and count only the approved posts in the topic (another bug), and check to see if the last post in the topic is newer than the last post recorded on the forum.