I think when the original post is deleted, the whole thread should be deleted too
I have seen this happen in the past. Personally, I think it is a bad thing, as it can be rather confusing, and also reinforces the draconian image of the whole reporting business. (Not to mention, it cuts off any general conversations the thread may have descended into...)
Your other suggestion, however, would be good, else it suddenly looks like someone else is the OP.
Null wrote:
At lest there should be a message instead of the deleted post
Clearly it is a race condition: A reply must not succeed without a parent message. I would imagine a lock is required in the database table that contains the forum threads in order to process delete statements.