Also, I shorted the battery negative to the threads, and the light does light, so it’s just the tailcap switch that’s the problem.
Re. the cause of the problem: Looking back at this thread:
where it says:
“Current regulation is via the internal resistance of the AAA batteries”
I’m guessing that since the IMR battery has lower resistance, there wasn’t any current regulation.
But seeing that there’s no physical damage to the switch PCB, I’m guessing that the switch itself may’ve been fried?
Jim