I know, famous last words, but hear me out. So I've had issues on and off with exporting out of Lightroom and into Photoshop. Sometimes the images export just fine, or rather any change is so slight that I cannot see it. But often with black and white photos that I've pushed to the extreme in the development module, exporting these files to Photoshop introduces strange banding and colour casts, particularly in darker areas. I had previously had Lightroom set to export files with ProPhoto as the colour space (yes, colour - get over it), and export a 16bit PSD. Likewise, Photoshop was set to ProPhoto as the working space, and to preserve embedded profiles. So I played around with the settings, and Lightroom's file export colour space back to AdobeRGB - the "wrong" colour space from what I've read on these forums, and indeed Lightroom itself advises to choose ProPhoto over AdobeRGB. But somehow changing back to AdobeRGB has resolved the issue, and the image in Photoshop is just how it was in Lightroom. But the question is, why is this so? As some background, I'm using a 27" Retina iMac running El Capitan, calibrated with an i1 Display Pro. The files are from an Olympus OM-D E-M1, shot using AdobeRGB as the colour profile in camera. Could it be that Lightroom is preserving AdobeRGB as the embedded profile?
 I've attached some crops of one of the problem areas. Note the green and magenta casts in the transition to black on the side of the highway. Oh and ignore the excessive halo along the edge, that'll be dealt with later. Also note the issue only appears in Photoshop under the conditions outlined above, it won't appear in a browser or file browser.