Last post date and user not updating after reply deletion on some topics.

1. Somebody has "grave dug" a topic from a few months back.
2. I delete the last post in the topic.
3. The topic remains "bumped" and still says the last post time and last poster was that of the reply which i just deleted.

This only happens to some posts but i can reproduce it on one of them right now. The post i can reproduce it on was created on version 2, and the last reply was posted after the migration to version 3.

attached is the row of the topic in question though i'm not sure if that helps.

Also, the topic has been moved from one forum to another but only after this problem was happening. (moved it to a moderator only area so i could test)