Wrong data in "my latest threads"

The info in the "my latest posts" section is wrong. For example, it reads:

Qt is good because...
last post by qgil - 5 minutes ago

The last post is actually by me, but on qgil. I've attached screenshots of the situation.

Investigating the other entries, it looks as if the "last post by xxx" is always the user who has started the thread, but not the user who added the most recent comment.