Ahh. Internally, songs with no artist specified have the artist value "</ unknown>" set by the local Android music library. I beautified this to "Unknown Artist" for the browser display. Now, when you click, it's probably pulling that name and searching the DB for "Unknown Artist", failing to return the songs by "</ unknown>" that are actually associated.
I also noticed that when you actually view all the songs you can see the unknown artists' music, but not when you click the unknown artists button. So what you said is probably the problem.
Ahh. Internally, songs with no artist specified have the artist value "</ unknown>" set by the local Android music library. I beautified this to "Unknown Artist" for the browser display. Now, when you click, it's probably pulling that name and searching the DB for "Unknown Artist", failing to return the songs by "</ unknown>" that are actually associated.