Something has changed between LR3 and LR4 in the processing chain for lens corrections. Doing an extreme correction (e.g. using a LCP for a fisheye lens) with increased contrast causes bad halos at contrast edges. The effect doesn't occur with the same settings on LR3. It is almost as if the LCP is being applied after the basic controls rather than before?!?!?!?!
So I did a bit more checking. It is actually the highlights slider that does it - contrast just makes it more obvious. It is as if the highlights "masking" is getting created in the pre-transformed data and then distorted in some way when going through and extreme LCP like with a fish-eye. Here is an example, contrast at 100 and the "Strong Contrast" tone curve used in both. The one of the left has highlights at 100. Notice the "shadows" in the sky of the leaves, as if the mask was somehow stretched differently from the image data. This was with a fisheye lens and fisheye LCP. You can actually recreate the problem to a degree yourself with any image. Just apply any of the fisheye lens profiles from Adobe (Nikon 10.5mm for example) and look at high contrast regions near the edges of the frame with highlights set to 100%. You'll see shadows like this (again, easier to see with extreme contrast settings). Without an extreme profile applied no such effect.
Hmm, can you please share your test image with me? I tried on a few of my test images, using Manual Distortion -100 or +100, and similar values for Horizontal and Vertical, to produce an extreme warp. I then cranked Highlights to -100, and/or adjusted Clarity to +100, and did not see any misalignment artifacts.
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Sure, I can. But it happens on every image (I use Nikon D80 raws, fwiw).
I could not reproduce it with manual distortions either, I used a Nikkor 10mm fisheye as the OP suggested.
I tried to repro this problem with D80 images and the Nikkor 10mm fisheye, but could not. Can you please send me an example image, with your adjustments? (You can also convert to DNG so that the adjustments are embedded, if you wish.)