Comment 11 for bug 322256

the first time you mark an expired message as unread, it's not in the read set,
so we think it is already unread.

we've got code that will bail out if you are trying to mark an unread message as
unread (or a read message as read). see nsMsgDatabase::MarkHdrRead()

still working on this... I think nsMsgDatabase::MarkHdrRead() is correct.

I need to investigate why the expired message isn't in the read set.