To reproduce:

1. Download attached project “ShaderTest.zip" and open in Unity
2. Open “test” scene
3. Press File > Build Settings...
4. Switch Platform to iOS or if you are using Mac then you can leave Standalone
5. Press Player Settings... and Other Settings check Metal Editor (Experimental) box
6. Observe that "Cube scale -1" gameObject in Game window becomes Green
6. In Hierarchy window select "Cube scale -1" gameObject and observe that it has a negative scale in X
7. Change its scale in X to a positive value
8. Observe that "Cube scale -1" gameObject in Game window becomes Red

Expected results: No matter what values is set in Scale, both cubes should be Red color
Actual results: If one of the values in Scale is set to a negative, gameObject will be Green

Notes:
- This issue only appears on Metal devices
- Changing two values in Scale at the same time cancels Color changing behavior
- If you disable Metal Editor Support (Experimental) then this issue does not appear in Editor but will appear on other Metal devices

Reproduced on Unity 2017.3.0a3, 2017.4.0f1 and 2017.4.17f1
Not reproduced on Unity 2017.3.0a2, 2018.1.9f2, 2018.2.19f1, 2018.3.1f1 and 2019.1.0a12
Regression on Unity 2017.3.0a3