Yeah... we meant to remove the editing features from the demo, but it appears some edits are partially working and removing files. We'll have to investigate it more, but I was able to put back the missing files so the demo works properly again.
My guess is that the demo theme editor wasn't completely disabled properly and it is removing some files when tested. I apologize for the inconvenience. Let us know if it happens again and I can fix it again. Better yet if the problem happens while you are playing with the demo, let us know what you did and then we can track down when and where it happens and prevent it from occurring again.