Another strange bug with D4, possibly D800!?!?

I think he understands that. The point he is making, I think, is that the exposure changes when he lets go of the AF-ON button. When he presses af-on the focus locks. When he recomposes the exposure changes as he expects it will and as you have pointed out. But when he lets go of AF-on the exposure calculation changes dramatically. Am I understanding the OP correctly?

--
Mike Dawson