Its a weird one, and avoidable too, but I thought I would mention it;
I equipped a pistol in my off hand and motion sensor in my main and turned the motion sensor on in my inventory. When i closed my inventory screen and pressed B to change to my pistol, I was instead changed to punch, with no gun image in my hand. I looked in my inventory and there was no pistol in sight, not on the floor or in hands or inventory. I closed inventory and pressed B again which brought up the motion sensor in my main hand and returned the pistol to my off hand slot.
Weird I know, and very circumstantial, but if it happened in combat lol, who knows.