In preview mode, if you scroll down and click on the About Us link, as soon as you get to the About Us page, the navigation disappears. You scroll down and it immediately appears, but disappears when you scroll back up. In the published version, it functions correctly.
It seems to be drawing some kind of interaction from the Home page even when it is displaying a different page in preview mode. Not really a big deal for this specific element in this specific project, but I would imagine it being a potentially big problem in other uses.