Yeah; the 'oriented'-ness definitely exposes the problem, (the sprite pans over time), though I don't think it's the source. Also, it would make sense that the sprite would seem brighter against an (even imperceptably) brighter background, though in that shot, the camera's stationary, and it's actually the sprite that's spinning, so the background is constant.
I'm almost inclined to believe that this is happening under A6 but not A5 -- anyone notice anything similar?