I never had WMR installed (I think) and for some reason two processes thought they might help me with motion smoothing. So I installed WMR, tried the above mentioned fix and voila, I don't have this problem anymore. Very strange, but fixed for me finally.
Also: I've read you also could try to delete "steamvr.vrsettings" in "\Steam\config"... as there might be some dead config lines from your earlier headsets etc. too...