System recovery through file deletion, AKA how many of cyrus' database files you delete to recover the mailboxes after a version change.
Literally, "right don't need that file it's only for deliveries in progress, delete it." "Don't need that one, delete it." "Hmm... still not recovering, let's try deleting those as well." "Ooh it's recovering the DBs now." And even better.... No ill effects!
Something about this seems sick and wrong.
Note, this was a copy of a server (with various version updates performed), not a live server.