How to reproduce :

In User,groups and rights, click on users
Select a user and click on impersonate button
A window appears. If I realise that I do not wanted to make this, I have no way to escape.
The close button does not work and if I a click on it or if I do not answer, the navigator become unstable : the processor of my computer is too solicited.

Furthermore, the window want that I confirm if I really want to make that but if I quit the application and I come back , the application has restarted with the impersonate account. So it asks me for something that it has already made ?