Steps to reproduce:
1) open attached project
2) create new scene
3) attach the 'NewBehaviorScript' to any of the GameObjects
4) press play
5) press 'Space'

Actual results: following error is shown
Scene '' (0) couldn't be loaded because it has not been added to the build settings or the AssetBundle has not been loaded.

Expected: The scene is reloaded. Or the error message should contain that the scene has to be saved.

Workaround: save the scene

Regression started: 5.3.0f4