<In reply to Top Bunk Tester's itch>
A good question. The only thing I can think of (I'm speculating here) is that with the aircraft in a negative g bunt your arm may not be resting on the armrest but floating somewhat above it, depending on the tightness of your harness and perhaps a bit of 'give' in the system. I agree that muscle memory would normally pick up on something like this, but from hanging upside down in a Pitts I also know that under severe negative g muscle memory is not totally reliable as the sensations are so different.