Animator window can not be closed down.

To reproduce:
- Create a new project and import the "Mecanim Example Scenes" project from Asset Store
- Open the "Generic Skeleton Example" scene
- In Project Browser, go to Controllers folder and double-click on "MineBot" Animator Controller
- In the Animator window - double-click on "Locotion"
- Create a new project
- Observe that you can not close the Animator window by right-clicking on the tab. And observe also the NullReferenceException errors in Console

Additional comment:
Workaround is to change the layout of the editor.