VRSettings.renderViewportScale renders sections of the screen oddly at values <1

1. When changing the renderviewportscale to anything other than 1 sections of the screen are frozen in place on the viewport, torn and warped. This was using multipass, openVR without any other post effects.

2. build and run the project (you can just select the start and viewportscale scenes if you like to speed up the build)
watch the scene through the different render scales

NOTE: I tried this with another test scene we have but could not repro it so there's something different going on in this scene but I can't figure out what.

this was found running case http://qatestrail.hq.unity3d.com/index.php?/cases/view/856 with our vr-test-suite project.

gif attached of issue for quick reference.