Oh, and just to make sure, you are just uploading the .pdx and not the entire contents of the zip?
I think this may be the problem -- the sideloading page should not accept this entire zip as a valid game. I've re-uploaded it as 2 zips (one with the game, one with the source). Try sideloading just the game one and see if it works!
Yes, this seems to have fixed the issue! Thanks! :)
