This is an oddball. At first, I thought it was a skin problem, but it looks like a core issue.

If you choose Advanced > Structure > Alphabetical or Calendar, added pages, like About.htt or Contact.htt, are ignored. No HTML page is created in the output. It's OK with Flat or the default Mirrored.

Still failing.

I think they should be put in the root, because that's where the skin navigation is typically expecting to find them.

That does introduce some problematic wrinkles, of course. A user might add an "about" page in each of several different folders. But that may not be worth worrying about - a user who is using regular folders in that manner isn't going to choose one of the oddball structures. More important that the basic case works properly.

Just did a few quick experiments, and not bad. For the most part, added pages, like About, are ignored when they're internally-linked (if the user has dragged it somewhere that way), and are ignored for view pages.

The only little oddity is that if you're sitting in one of the alphabetic folders, for example, and you click the link in the navigation bar for the About page, and then you choose "up," you're taken to the main album, not to the alphabet page you just came from. I'd call that "too minor to worry about."