I tested this MD script on the A720IS. It is the first one I can actually get to work so that's great. What I'm curious about though is when the script if running it turns on the focusing light. Why does it need to do this? Is there a way to turn it off. It really drains the batteries quickly.
The script does not control the focusing light (Ae beam) in any way. If (when) the script lets the camera autofocus, it flashes the light just like it always does unless you disable it from Canon's menus (this is the easy fix to your problem, of course).
I haven't noticed the Ae beam getting stuck in any operating mode of the script on my camera, but this doesn't mean your camera wouldn't be different. Yours is a DryOS Digic III, mine is VxWorks Digic III.
Now, we need more information.
Try both still shooting operating modes (fast and slow) of the script and in different camera modes (such as auto focus, manual focus, M mode, P mode). I'm guessing the Ae beam only gets stuck in fast react mode and that this problem doesn't exist in slow mode. In fast mode, the script runs motion detect while the camera shutter is half pressed. In slow react mode it doesn't press the shutter at all until it has detected motion.
Maybe your camera doesn't find focus and that's why it doesn't turn off the light (but isn't there a timeout in the camera for finding focus?). Or, maybe your camera always (unless disabled) keeps the light on while half-shuttering unlike my camera, which only blinks it during autofocus (you can test this even without CHDK).
