Steps to reproduce:
1. Open user attached project (New Unity Project 2)
2. Open Scene.scene
3. Notice a cube with cutout circles
4. Build and run the game
5. Notice that a square is displayed instead

Expected result: when cutoff variable is not defined, alphatest value should be 0 in the editor
Actual result: when cutoff variable is not defined, alphatest value is not equal to zero

Reproduced in: 2017.3.0a1, 2017.2.0b4, 2017.1.0p2, 5.6.2p4, 5.5.4p2, 5.5.0a6
Not reproduced: 5.4.6f1, 5.4.0b7
Regression since: 5.5.0a6