Inconsistent login between bitbucket.org and custom domain

I set up a custom domain to my bitbucket account and it works fine, except that if I'm logged in on the main site bitbucket.org, I am not on my domain, and vice versa.

To sum up, login works fine, but separately on the main site and my domain.

(This bug concerns only simple login, not the openID login, as there is another problem preventing from logging in with openID on a custom domain. See issue BCLOUD-2007)