Viewer Does not update rendering

[ptbremer]

With commit 298224b on master on my 10.12.6 Mac OS. The viewer does not update the rendering during the progression of a slice. If you move the slice it will show you a simple gradient that only gets replaced by the actual data if you perform some action. That can be a rotation a mouse click or even a loss of focus of the window (which is why I cannot even take a screenshot)

Trying other branches and checkouts with similar results