Steps to repro:

1. Launch Unity on OSX;
2. Open attached project;
3. Go to Assets -> Scenes;
4. Open 'Main' scene;
5. Open Build Settings;
6. Add open scene by clicking "Add Open scene"';
7. Build the scene for Standalone platform by clicking "Build&Run";
8. In Player configuration check 'Windowed' checkbox and click 'Play'.

Actual result:
After splashscreen glitchy artifact appears. See attached video.

Regression introduced in Unity 5.5.0b8.

Expected result:
Scene launches smoothly without artifacts.

Notes:
- Reproducible in 5.6.0a1, 5.5.0b11, 5.5.0b10, 5.5.0b8;
- Not reproducible in 5.5.0b7, 5.4.2p2;
- Reproducible only on OSX 10.12.1 on MacBook Pro with Intel Iris GPU;
- Not reproducible on Windows 10;
- Reproducible only in Windowed mode; not reproducible in full screen mode.