I've created the page, and everything works except that users are no longer logged in when visiting the custom page. Clicking any tab or link to navigate away from the page brings me back to the normal logged in state, but the custom page is logged out. How do I fix that?
edit: Found the problem. It's a privacy policy page, and in Options > Site Name / URL / Contact Details the link to the page was the full path (
http://sitename.com/forums/privacy.php) instead of relative (privacy.php). Once I made it relative it worked fine.