Bug seems to be introduced in: Version 5.6.0b2 (5d236ef0678a) Tue, 06 Dec 2016 10:45:15 GMT
Branch: trunk
Checked against DX9 - Which works fine.

Steps to repro.

1. Open attached project
2. Build for win standalone.
3. Run player, try a low resolution like 720 x 480
4. Toggle windowed mode to true.
5. Press play, wait for splash then press alt+enter and observe results

Tested in: (Broken)
Version 5.6.0b3 (358ff4ed3952)
Thu, 22 Dec 2016 12:29:14 GMT
Branch: 5.6/release

Tested Against: (Broken)
Version 5.6.0b2 (5d236ef0678a) <--- bug introduced here.

Tested Against (WORKING)
Version 5.6.0b1 (d37b23d9dfff)
Tue, 06 Dec 2016 10:45:15 GMT