BUG: VR.WaitForGPU forcibly occupies CPU when running in background

I'm working on a enterprise-level Unity3D project on OpenVR recently. Generally speaking it works great, yet when I send it into background (when other VR programs are running) Unity forcibly cooled FPS down to ~10. I've noticed that VR.WaitForGPU used ~100ms even if there are nothing being rendered. No active cameras.

I know there are no needs for rendering to HMD when you are in background, but what if I need it to be in companion window while I cannot even toggle off VRSettings.enabled?...

BUG: VR.WaitForGPU forcibly occupies CPU when running in background