Thanks John,
I've seen similar behaviour, but it looks more like a bug rather than just the amount of work being done. Current consumption when running is around 80mA, but I would see it jump by approx 100mA intermittently for a few seconds. No effect on motor speed, and the extra current was still there with the motor stopped. This is about 1W that has to go somewhere, and is basically heating up the chip until it trips.
For me, turning off RailCom stopped this happening. Turning off Mfx etc made no difference.
It's not specific to the Class 128 - I have a Farish Class 40 and Rapido Class 28 with the same behaviour.
Neil