Simultaneous login on 2 WordPress sites with same user credentials.

Hi,

I have Linux hosting for dnb2b.in and also an add-on domain dnb2b.us at the same hosting account.

I installed separate instances of WordPress 2.8.3 at the following 2 locations:
http://dnb2b.in/showcase/
http://dnb2b.us/showcase/

Unwittingly, I used the same admin user and password for both. While adding post on the .US version I browsed the .IN version in a new tab and it came up already logged in (I had clearly logged out of it earlier). I have since changed the passwords for both, but I believe this is a bug/loophole fit to be addressed.

Must be something with the session cookies. Just for reference my browser is FireFox 3.5.2 and OS is Windows XP Prof.SP2.

Any ideas on how to prevent this? Apart from having different passwords of course 😉

Thanks.