Login button on 404 pages for subdomains don't work (BB-11935)

If I head to a nonexistant subdomain such as username.bitbucket.org and click login I get a URL like this http://username.bitbucket.org/account/signin/?next=/hosted/omgimalexis/account/signin/%3Fnext%3D/hosted/omgimalexis/account/signin/%253Fnext%253D/hosted/omgimalexis/ and it just keeps adding the redirect link to the end as I click the login button each time instead of going back to the base URL bitbucket.org with the login link at the end.