I was processing a bracketed set of shots and playing with the ACR Lens Correction "Upright" options. I got significantly different results for the same option on different exposures (of the same image). Tried it on a different set and it didn't happen. Got the same results on each exposure.
Baffled at first, but then realized why. The Upright otions look for horizontal and vertical edges in the image. On highly overexposed images, some of those edges might disappear. The Upright adjustment operates only on what's left.
On an overexposed frame I adjusted exposure, shadows, highlights to make the edges look similar to the normal exposure frame and then applied the "Auto Upright" lens correction. No change. Got the same result as without exposure corrections, which tells me the lens corrections happen on raw data BEFORE any exposure adjustments are applied.
