When opening files shot with a Pentax 645Z in LR 5.7 I have very strong (overlighted).
Updated camera raw to 8.8: no change.
I don't have that if I disable the profile correction.
If I set the vignetting to minus 5 it's fine… but not normal!
Forgot to say that I'm on Mac, Yosemite OS
nic_C, this should be fixed in the next version of Lr (updated profile).
Note that updating ACR versions (e.g., 8.8) will have no direct impact on rendering of images in Lightroom. This is because ACR and Lr are separate (though related) products.