The reason the person's handle still shows up as making the last post in a thread is that, as much as you might wish , you didn't obliterate the person by placing them on your ignore list. They still exist for everybody else's viewing pleasure...you just chose not to personally see their commentary.

This is not an item that, IMO, TB has much control over. Perhaps it might be better switched to Technical Issues so that the HOM's/IB staff can weigh-in. Perhaps there's something with this or an upcoming edition if the vBullletin software that drives this board which may address your issue.