I think this is a clue:

When I opened a new animation document, it automatically had a small white background that I am noticing now appear to be the same dimensions at 480x320px.

I didn't think anything of it because there's always a white background whenever I open up any new document. But when I save/export things, they never pick up that white background. I've always thought that was just the working desktop.

But it would seem that the export is actually including that white desktop background.

Does that seems right? How do I get rid of it?