To reproduce:
1.Open attached project.
2.Open and play "Scene.VR Bugs" scene.
3.Press "Space" key in keyboard, settings panel should appear, change "Render Scale" slider.
4.Console should output current renderTexture size, when we increase render scale and then decrease it, notice that renderTexture size stays at maximum value it was, instead of decreasing in size.

Additional note:
It seems like in 5.3 alpha re-rendering renderTexture after RenderScale change takes a lot more time than in 5.2.