Steps to reproduce:
1. Download the user's attached project
2. Go to Edit->Preferences->General and make sure "Verify Saving Assets" is enabled
3. In Project Window, go to Blocks folder
4. Select Grass Material
5. In Inspector window, change The Albedo from White to Red
6. Press CTRL + S
7. In the "Save Asset Window, press Save All
8. Repeat step 6, notice how the exact same assets are marked as "Modified".
9. Quit Unity
10. Open the project again

Expected: Grass material albedo is Red (Behaviour described in step 8 should not happen)
Actual: Grass material albedo is still White.

Reproduced on: 5.5.3f1, 5.6.3f1, 2017.1.1f1, 2017.2.0f1