I was going to ask about the same issue - hopefully I'll be able to fix it with the solutions suggested in this thread (will have to wait this evening) because I had not been able to enjoy WOFF UE so far because of that (didn't try unplugging HDMI and plugging it back - since I couldn't get my screen back from black I would trigger a power off of the computer then turn it on again...).
Neat, now I'll be able to go back experimenting with VR support (currently just going to try setting up dual viewports for the stereo 3D with the hope that openTrack will support Vive soon enough to start with that instead of my own implementation of head tracking)

Edit PS: nice, that sorted it entirely, no more issues now!