I tried "click('zoom_in')" on single camera and that works for about 5-6 zoom steps and then camera crashes (Powers off with lens extended without any error display).
That's something that should not be happening (you can retry the experiment manually, without CHDK, if you want - that would rule out a firmware bug). I don't see obvious CHDK involvement in the log, but I could be wrong.
The log appears to show however, that the cam tries to enter playback mode at the same time when the zoom lever returns to its normal state. I don't know why that would happen.
For the power, I'm using the batteries supplied with camera at the moment. It's soooo tedious to charge so many of them so will be considering AC power soon.
I suspected an issue with a shared power supply, so that's obviously not the cause.