It looks like your DNS and hosting are both at godaddy. I would definitely check there first.
The "mobile" subdomain is probably a default subdomain that you magically get when you sign up with a domain through them. I have a client who had a very bizarre domain forwarding issue based on what godaddy was doing at the DNS level, and I'm curious if maybe they are doing something similar in your case. Their system may be doing a mobile device detect before deciding whether to keep the request on www or send the user to "mobile" instead.
It's just a theory, but it's definitely where I would start if I were you. WP isn't going to do that by default, and you've already ruled out the theme by talking to the author.
Good luck!