[DonRotolo]

OK, Thanks.

From the markings I see on the central "lumps" of the clear side of the belt, I theorize that the belt slid sideways on the wheels, so when the drivetrain was powered up they rode up onto the wheels. This stretched the belt to catastrophic failure. I am thinking that an under-tensioned belt could do this.

I am not trying to cast apsersions or 'blame'; just hypothesizing (= guessing) as to how this might have happened.

Anyone else have a theory?