When using RenderTexture on camera and there are scene objects using GrabPass shader, the RenderTexture becomes black. Even with AA disabled (!).

Steps to reproduce:
1) Open the latest attached project.
2) Build for iOS.
3) Run on a Metal-capable device.

A colored cube appears in the scene surrounded by black background, however with OpenGLES, transparent area (skybox material) is surrounding the cube. This happens because the camera's RenderTexture becomes black. Replacing the GrabPass shader with some other shader on the 'Cube' GameObject fixes the issue.

Note: the same issue occurs when AA is disabled in the QualitySettings.

Reproduced on:
5.6.0a6, 5.5.0p1 (older versions fail to compile the GrabPass shader).

Devices:
iPhone 7 iOS 10.2