Answer - you can correct horizons, but you can't correct reflections.
I shot these yesterday and the ball head I'm using (Manfrotto pistol grip ball head with the grip to the side) wouldn't level out enough. I figured, well I'll correct horizon in post - no big deal....now, I have reflections that should be 90 degrees but now are angled.
Another image with the sun already set, no apparent offset reflection.