Steps to reproduce:
1. Create a new project
2. Turn on VR in Player settings
3. Create 2 cameras
4. Set one to Left eye
5. Set one to Right eye
6. Enter Play mode

Expected result: view is rendered as normal
Actual result: only 1 eye is rendered, the other is a black screen

Reproduced with 5.6.0b9 with Oculus and HTC Vive
Not reproduced with 5.5.1p4

Notes:
-Upon disabling/enabling the other eye renders and keeps the frame it sees at that moment