Please describe the problem:
if you select view unread messages in a folder, any messages which are
subsequently marked as read, will disappear when you go back to view all messages.

Steps to reproduce:
1. select View | Show Messages | Unread Messages
2. read all those emails, and make sure they are all set as unread
3. select View | Show Messages | All



Actual results:
basically, it looks like if you are viewing unread messages, and then switch to
viewing all messages, any messages that had been read will disappear

Expected results:
it'd be nice if messages didn't just vanish

Does this happen every time?
yep

Other information:
first, i'm using exchange, and i didn't test IMAP.  second there is a workaround
provided you can access the emails another way, either through a vFolder, or
through another mailer or OWA.  mark all the emails unread, and select view
unread messages only again.  now you can see them again.  make sure they are all
marked unread, and then change back to view all messages, and they are back.