So these issues on OFW 2.1.7 may present for others as well... Needs further investigation. This PQ issue you had is called "banding" BTW.
I will do the S&M banding video test today, but I'm only able to do on 1080p, as I don't have an UHD TV yet.
I guess the CFW uses different version of the HiMedia Video Player (maybe the 1.2.53 version as the OFW has the 1.2.57 version for sure). Maybe pcristi can reassure these...
Edit:So I have tested with OFW 2.1.7 and 
with this S&M test video (seen on the bottom part of the page) there are no Banding issues with 1080p /YCbCr 444/ 10bit on 23.976Hz. But according to the test description (if we take it seriously), it fails on the 
Clipping and 
Scaring tests (the little square boxes inside all the color rectangles are not visible). Tho' I don't know how much this affects the overall video playback PQ in practice... I have also tried it on all colorspace/bitdepth combination available in the Advanced menu, but none were better concerning the Clipping and Scaring test. Wonder how could the CFW perform regarding. 
