Reproduction steps:

1. Open "SceneUnloading.zip" project
2. Enter Play Mode
3. Click on the most left button
4. See that four Scenes appear in the Hierarchy and they disappear after being loaded
5. Press the middle or most right button
6. See that Scenes appear in the Hierarchy

Expected Result: The "D" Scene should be loaded, but not Activated and all other Scenes should load after that
Actual Result: The "D" Scene doesn't load and stops all other Scenes from loading

Reproduced with: 2017.3.0b2, 2017.2.0f1, 2017.1.0p3, 5.6.3p4, 5.5.4p5