I have also been in an accident where my Speedplay X pedals automatically released. Because I hit my head, I don't remember any of the flying upside down part, but the bike and I were a several feet apart when I found myself on the ground with a broken clavicle. I doubt that the pedals release just because you are upside down, since the mechanics are very simple. Maybe they release at a high enough force or impact. Look and SPD pedals have an adjustable tension setting (too light and you might come out while pedaling hard, too tight and you might not get out when you stop).