Steps to reproduce:
1. Open attached Unity Project in comment "SimpleRepro.zip"
2. Load Scene "Stencil_SetShaderGlobal_Bug"
3. Enter Play mode
4. Click on StencilID = 0, StencilID = 1, StencilID = 2 to see that each button mask out the sphere differently (correct)
5. Exit Play mode.
6. Load Shader script "Shaders\StencilGlobalDiffuse"
7. Change "ZWrite [_GlobalZWrite]" to "ZWrite On"
8. Enter Play mode again
9. Repeat step 4 to see nothing happens (wrong)

Expected result: Stencils would get updated both via script and via property block in the Inspector.
Actual result: Stencils do not update until the global ZWrite state or another Stencil state is updated.

Reproducible with: Unity 5.6.1p3, 2017.1.0b1, 2017.1.0b6, 2017.1.0b10, 2018.3.0a8