I am not sure if anyone from amd driver team reads this forums, but its worth a try.
I have MSI 270x hawk with standard clocks 1150 gpu/1400 mem mhz (1150 is boost clock which is kinda default anyways).
If I use DXVA in potplayer, GPU never goes to 2d clocks (300/150mhz) and stays in 450/1400 mode. In games, clock rises to 1100/1400 (which is non-boost clock) unless I restart driver by disabling/enabling gpu in device manager. OCing is impossible during this driver-state and only fan control works. The most interesting part is that GPU-Z shows PCIe 2.0 instead of 1.1 (yes, I still use old MSI K9A2 Platinum with 1090t).
Also, Im not the only one affected by this issue, another member of benchamrk.rs forums reported same issue with his 7970 with Z77 board (which has PCIe 3.0).
Obviously, gcn 1 cards are affected, and I will check tommorow with another friend if he has same issue with 280x (even if it is same chip as 7970...)
16.7.2 works fine