I just found out the the 'Delete' button at the top of each PM conversation page doesn't just delete that conversation.

It deletes _every_ _private_ _message_ _you_ _have_ _ever_ _received_!!

That, to phrase it delicately, is not quite the expected behaviour. It is certainly interesting behaviour, but perhaps somewhat less than optimal. I think that if you are going to have it behave that way it would be a very good idea to mention it on the 'Site Features' page.

Edit: Aha! It doesn't, but the current behaviour is still VERY misleading.

If I delete the oldest PM conversation (which hasn't been relevant for ages) I get the following message:

''No current private messages for your member account. If you also have a listing (nursery, breeder, etc.) you should check the Private Messages tab there too.''

Note the first sentence. It clearly says there are no private messages. The page this notice is on reinforces that message, because even if you refresh the page there are still no private messages shown (at all).

However, having gone away overnight and checked my PM's again this morning, I now find that the rest of them are still there.

So... the problem is the highly misleading message that is persistent through page refreshes.