Sam, what seems to be happening for me is that when I answer a thread, I become unsubscribed from it even though I've checked the 'notify me' box. Maybe the logic of that box has become reversed? I'm going to try unchecking the box for this reply (I habitually leave it checked) and see what happens.

Edit:

Yes, that did the trick. If I check the box, it unsubscribes me; if I clear it (as you do) it subscribes me. Good grief.

There's your workaround, anyway; tell the forum to do the opposite of what you actually want.