support www subdomain.
EDIT: I've found the issue, Cloudflare quirky setup. It works with www, too.
This feature won't probably be implemented too soon but I will keep the ticket open.
The reason why this isn't implemented is because from the user experience point of view acessing your site as domain.com OR www.domain.com should lead to exactly the same content. This is the recommended way to server your website content and you should redirect the non-www version of your site to the www version.
So, by not implementing this "www" support userTrack "forces" the webmasters to follow the best-practices in order for it to work properly.