This is an old issue, and it's been brought up several times.
You're not supposed to name your AD domain, the same as your public domain. Given that renaming your internal AD is, let's just say "challenging"...
In short, you can't fix it.
I've heard of a suggestion where you create a web server on your primary domain controller, and redirect it to www.<your Opens a new window Opens a new window domain name>, but I don't know if that's still recommended (I think it causes other issues), and it's not recommended to setup a webserver on your PDC (because it may be used for other things).