Steps to repro:

1. Open attached project;
2. Go to Assets -> _Example Scene(import recommended);
3. Open scene 'ExampleScene(Gamma)';
4. Launch Play mode;
5. Lower terrain to zero level by pressing down arrow button in the UI;
6. Observe Game view and console.

Actual result:
- 'maximum ps_4_0 sampler register index exceeded' is thrown in the Console;
- Prefab 'Horizon[ON]_Cliff_Example' is all pink-colored.

Regression introduced in Unity 5.6.0b5 (bc8585c89061).
See attached video and screenshot.

Expected results:
- No shader errors are thrown;
- All objects should be rendered normally.

Notes:
- Reproducible in 5.6.0f3, 5.6.0b9, 5.6.0b5;
- Not reproducible in 5.6.0b4, 5.5.0p4, 5.5.0p1;
- Reproducible on OSX 10.12.2 and Windows 10;
- Reproducible only in Editor, not reproducible in Standalone player.