Steps to reproduce:

1. Open attached project
2. Open Assets/Scene.unity
3. Open Assets/Script/TestCode.cs with Visual Studio
4. Put a breakpoint at line 19: Debug.Log(n);
5. Press "Attach to Unity" to start debugging
6. Switch to Unity editor and press play
7. Press 'MyCoroutine()' button in Game View
8. Visual Studio halts at the breakpoint
9. Inspect the value of the variable "n"
10. Notice it shows the value of 5 while it should be 1 (as it is printed in Cosole with Debug.Log)

Reproduced with: 5.1.4f1, 5.2.3f1, 5.3.0f3, 5.4.0a4

Tested with: Visual Studio Ultimate 2013, Visual Studio Community 2015