Are you sure that there is not another protected by roles page that is actually the first page in your site?
The "home" link in the top nav just points to the root of your site, if the first page in your site is protected by roles it will redirect you to the login page. Clicking home in your site map seems to work but that url is /home.aspx it may not actually be the home page. The home page is simply the root level page with the lowest sort order but if that page is protected by roles it should redirect to login. The page with the url /home.aspx does not appear to be protected but it doesn't seem to really be the home page as defined.
Have you specified a different login page in web.config or user.config?
It should not be redirecting to /login.aspx that results in a 404, the correct login page should be /Secure/Login.aspx
You may also want to review url manager and 301 redirect manager for any unintended or incorrect things.
Also make sure that /Default.aspx is the highest priority default document.
Hope that helps,