Hi Tom as you say it only ever seems to appear under "extreme conditions"
I've heard of customers complaining their brakes all but disappeared when going over and down some of the very steep passes in the Lake District only for the pedal to return when things have cooled down. The only casualty I've seen was myself when I used to rally. Using standard pads and shoes the fluid boiled and I ended up going through a fence. The event photographer was on hand to catch the moment.
So I guess you’ve got to doing something out of the ordinary to get a failure.