Reproduction steps:
0) See gif attached in the edit.
1) Open attached project, proceed to scene 1.
2) Open "GameSettings" script in Visual Studio 2015 (14.0.23.107.0 D14REL).
3) Place break point(F9) at the start of Awake function.
4) Hit, Attach to Unity button and go to play mode in Unity.
5) Once code reaches breakpoint in VS click F11 to move down the code.
6) Hit red square ("Stop Debugging").
- Unity should crash.

Note 0: 5.1 Does not have "Attach to unity" button in VS UI and thus debugger is attached through Debug > Attach Unity Debugger. This does not result in a crash when stoping debugger. Also if you use this way to attach unity debugger in later versions it also does not crash the Editor.
Note 1: Pausing and then stopping debugging does not crash the editor.
Note 2: Does not crash with MonoDevelop 5.9.6

Reproduced with: 5.2.4f1, 5.3.1p3, 5.4.0b1