Steps to reproduce:
1. Download and open attached project "sbar loadSceneAsync test.zip"
2. Open and play scene "_Project/Scenes/GUI"
3. Notice that "Load Scene 1", "Unload Scene 1", "Load World View Stripdown" and "Unload World View Stripdown" work as intended - they load and unload scenes

Pressing "Load World View" does load the view as expected, and you can unload it by pressing "Unload World View" but only once. Every other time you try to load that particular scene it stalls at 90%. After that no other scene loads at all too (gets stuck at 90%)

Expected result: Scene loads and unloads all the way

Tested and reproduced on:
Windows 10
Unity 5.3.2p4 5.4.0b7

Not reproducible before 5.3 because SceneManager did not exist prior.