What I see in your non-default skins is that the 'nav buttons bar' bit was moved above the 'breadcrumb, login, pm info' bit, from the navbar template to header template, but for the default skin, looking at the HTML source, the only thing for 'nav buttons bar' I see is the following:
Code:
Content visible to registered users only.
PhotoPlog wouldn't affect how your forumindex.php page looks, unless you add thumbs, so I'd say that the 'nav buttons bar' bit wasn't moved to the header template in the default skin, but rather it was just deleted from the navbar template and that's why you don't see it.