On iPhone 6 Plus and 6S Plus, when shader performs un-premultiplication of a pre-multiplied texture, all the transparent areas turn opaque black.

Steps to reproduce:
1) Open the attached project.
2) Build for iOS.
3) Deploy on iPhone (6, 6S, 6+, 6S+).

There are two textures in the scene. The left one has un-premultiplication applied via a shader. The transparent areas of this texture are completely black. The texture without un-premultiplication doesn't have this behaviour. This issue only occurs with Metal as the Graphics API.

Reproduced on:
5.6.0a6, 5.4.3p2, 5.2.4f1

Devices that reproduced the issue:
iPhone 6 iOS 10.0
iPhone 6+ iOS 10.0
iPhone 6 iOS 9.0.2
Did not reproduce on:
iPhone 7 iOS 10.2
iPad Mini iOS 9.3.5