A much better explanation is what I said above, what I was being told before someone told me this made little actual sense. Reverse current when braking makes perfect sense, and it is something I've actually seen on a scope. That's the way it was explained to me recently in both forums and person. Even the very first brushless ESCs did this. It's not that the capacitors won't stay charged up, it's that they overcharge (overvoltage) and this causes failures.