Yes, strangest thing, never had it happen before. I'm using OS X 10.12.3, with the AMD Radeon 455 and Intel HD 530.
Tried quit and restart a couple of times then out of the blue I decided to maximize the gamma window in the workspace and then
resize back to the quad view and viola!, problem solved. All I can think is something got hung up with different window sizing or one of those weird
gpu artifacts. All good for now.