How to reproduce:
1. Download and open attached project file
2. Open "main" scene
3. Play the scene

Expected result: The red sphere uses a shader that sets stencil values. An image effect is applied to the camera that is supposed to desaturate the image except for pixels where the stencil value has been set, so the red sphere shouldn't be affected and should continue to appear red.
Actual result: The red sphere is affected and appears gray.

Reproduced with: 5.6.0a1,5.6.2p2, 2017.1.0f3, 2017.2.0b3
Not reproduced with: 5.5.1f1, 5.5.2f1, 5.5.3p2
Regresion since: 5.6.0a1