[MlMt] Odd behavior when deleting and recreating an account

[Steven M. Bellovin]

One of my accounts was being moved to a new server in a way that would 
not preserve the IMAP UIDs. Accordingly, I deleted the "mail source" 
entirely. (Aside: that it's called "mail source" for deleting or 
renaming, but "IMAP Mailbox" for adding is unfortunate.) I then added 
the account anew, but of course with the same email address. That 
worked, but...

Under "Sources", the recreated account shows four unread messages in 
Inbox. That's correct, and corresponds to what I had before the 
shuffling. However, in the unified Inbox, the sub-folder for that 
account shows no counter, i.e., no unread messages. I have a smart 
folder under "Inbox" for unseen messages; its subfolder for that account 
also shows zero--but when I open that folder, I do see those four 
messages. In other words, the smart folder knows which the four unread 
messages are but doesn't know how to count them. Huh? The "Displayed 
Count" setting for it, the parent "Unseen" folder, and the unified inbox 
itself all say "Inherit"; the other folders under "Unseen" all display 
the correct count of unread messages.

I've seen this on two different computers. On one of those two but not 
the other, deleting the source deleting the corresponding folder under 
Messages/IMAP; on the other, it did not. (I renamed it to get it out of 
the way.)