I believe what you are referring to is the clipped highlights of the Blu-ray when played on most (all?) players. The only explanation I have is that when originally encoded, the highest value was 255 rather than broadcast safe 235, so when players ‘expand’ the values, anything above 235 is clipped. Therefore, you must import an unconverted transport stream of the Blu-ray into your editing program and bring the highlights down before making further changes. I’ve tried to convert the Transport Stream into RGB in avisynth with a contrast reduction before the RGB conversion to see if it would retain the highlights, but no dice. The only method that I’ve found to do this is bring the TS file into Premiere and use a curves adjustment, which operates in the YUV colorspace. Perhaps you have a better method of doing this.

Regardless, I’ve found that virtually all of the highlight information exists in the Blu-ray data. Now if only there was a way to recover the superblack detail.