Same cookie name, different domain

I have:

Code:

$config['cookie_domain'] = '.' . $_SERVER['SERVER_NAME'];

So why do I have one cookie named ci_session with the domain:

Code:

.mysite.com

And another cookie named ci_session with the domain:

Code:

.www.mysite.com

And also, is this a problem. If not, I don't care why it's doing it! Ha!

This is version 2.0.2 btw