I ran my MMM on 10S

[BrianG]

There is a TVS device that is set to trip just a little higher than 6s voltage (~26v IIRC), so you most likely popped that device, but you should have noticed a larger than normal spark when it blew. And the main caps are only rated for 35v (10s is 42v freshly charged). It's a good think component manufacturers design in a bit of overhead, but who knows what else you overvolted!