I’m having a similar problem. I’ve already created an index.html file in the mydomain.com folder.
This index file works if the site is accessed through http://mydomain.com. However if I try http://www.mydomain.com, I get that empty directory listing. Manually going to http://www.mydomain.com/index.html brings up the correct page.
Am I missing something? I’ve tried to manually add “www” as an additional subdomain but got a response saying that it is already in use.