That was quick! The folks at Euphonix are already out with a patch that resolves an issue with the just-released update Mac OS X 10.5.7. From the description:

Software update for both MC Control and MC Mix that fixes compatibility issues with Mac OS 10.5.7. Includes recent MC Control touch-screen response optimization, as well as improved Digital Performer integration and more.

http://euphonix.com/artist/support/downloads.php