I have found this comment on DPReview about Yongnuo YN568EX on Nikon cameras:
Can anyone confirm that high-speed sync doesn't work on Nikon version of this flash?
Great - EXCEPT FOR AUTO FP. Regardless of what the advertisements say, these flashes are not fully compatible with Nikon. These flashes are designed for Canon. If you want a basic flash, then the 560s are a good deal. DO NOT get this flash if you have a Nikon, and are interested in Auto FP (HSS in Canon-speak).
Can anyone confirm that high-speed sync doesn't work on Nikon version of this flash?