Okay, I now see this is intended behaviour I'm not really happy with. The reason is that deleting a posting A would result in all replies to posting A becoming orphans.
This is an issue in Threaded Mode, but no one at our forum uses Threaded Mode. We all use Flat Mode.
I propose this solution:
Implement a check box in the admin panel that enables you to choose between the current way of deleting postings or actually deleting said posting and moving its orphans one level higher.
