The newer versions of the MM use different FETs than the old MMs so it might be possible that the logic circuit disables the ESC at anything over X voltage. The old ones use the same exact FETs as the Quark 125, but the newer ones are different.
Here is a thread that discusses the differences between the old and new versions:
http://www.rc-monster.com/forum/showthread.php?t=6349