IE Back button Cookie issue

[mocsharp]

To reproduce the problem, first you log on with admin/123, then click Log out from the nav. Now, click on the Twitter login button but DO NOT login, simply click the Back button on IE, you will see the user is still logged in.

The problem is IE writes the existing cookie when you go back to previous page.

[mocsharp]

The fix is to delete the cookie on the server side.