I've had the very same ugly behavior, plus flickering of the OSD in fullscreen mode.
I tried various versions of FFMPEG, without avail.
At that time the versions of the driver and libva were differing, i.e. 1.7.1 vs. 1.7.3 (Kubuntu 16.4), since there is no way to get newer drivers into the system - at least to my knowledge.
After upgrading to 17.04, both are aligned (1.7.3) and it works flawlessly (FFMPEG V3.2.4).