I just released a new version with several bugs fixed, both physics bugs and other problems. See bug tracker or github commit list for details.
I renamed bitmap/ to images/ and converted all "official" images to .png. If you have terrain which neither geoo nor me is tracking, then you have to copy that manually into images/ (no need to convert to .png). Also, I renamed replay/ to replays/, again you can copy over your old stuff (but I had physics changes in the current release, so it's not as important to keep old replays).
Proxima: I could reproduce the problem (editor exit & save), this isn't fixed in the just released version, but I will do something about it. New versions will be out quicker than the current one when they don't have physics changes.
-- Simon