Ha ha!

I just scrolled up and looked at the schematic again. And if you actually wired it that way, then it makes sense now.

I put the voltage sense on VDD instead of the batteries. That way there's no leakage through the diodes. And, since you have a reference that is independant of VDD you should be able to tell when the batteries are too low to hold the regulation point. But, my previous explanation is probably what was happening before.

What a memory, NOT!

Darrel