As a side note if you have another account logged in on the forums it will log out the one that was previously logged in.

For example

I am normally logged in as Stance. I decide to join a clan on my alt and open a new tab for the forums and log in as Buttmannz(since you have to log out to do this), it will log out stance.

I think. Im gonna test this right now- Tested,it is indeed like this^^