Cross browser cookies

I am working on an app which has a cookie login. Nothing exceptional.

But I encountered a strange behavior. I was testing some of the apps internals and for that purpose I had four different browsers open. After cleaning the browser history, cookies and everything - Starting with IE as the first browser I was required to login. Good.

The next browser went directly to the content - and they were logged in with the same username/password combination I used to open the first browser. I was certain that all browsers kept their own cookies.

Anyone seen this before?

The browser used in this session was latetest Firefox, latest Chrome, latest Opera and not to forget lastest IE.

All executed on Win 8.1preview.

Now Opera look and feels very much like Chrome (same codebase?) but the others should definately not log me in with another browsers cookie. Not to mention the fact that the cookie is encrypted and only the app knows how to decrypt it!

I am confused - very much confused. It should not happen! Any ideas are welcome.

Thanks in advance for any light You clever people can shed on this matter.

I have checked to see if I screwed something. These are the steps taken:

 - Opened the four browsers
 - Cleaned cookies and everything in all four browsers
 - Opened the app's login page in all four browsers
 - Using IE to login - check to save cookie.
 - Refresh the login page in the other browsers

Result:
Refreshing the 3 browsers revealed that they read IE's cookies for that specific hostname.


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