I ran into an interesting problem when I uploaded some cover art. After I added it, I realized that I had not checked the "Front" checkbox, so it didn't know what kind of art it was.
When I downloaded the cover, it was saved as "unknown" (makes sense). I went back and check the checkbox, but it would still save as unknown. I assume I would have to wait for that edit to finish before it would get renamed.
I got tired of waiting, so I deleted it and re-uploaded with the front checkbox checked. Worked great then!