SBCHAVEL I have worked around MUM's "launch when Mail launches" setting. Using the great keyboard shortcut app iKey, I set up a shortcut so that when Mail launches, 3 seconds later MUM launches. This time delay has ended MUM's automatic quits. For those of you who use other shortcut apps (e.g. Spark), you may want to experiment with them. When MUM works, it has better features than all the other unread-mail-tracking apps.
(Version 3.1.1)