On more than one occasion, I have lost all edits to a song by using CTRL+Z during the editing process. It will close the current song (without saving), and replace it with the previous song in the directory and there is no going back. As CTRL+Z is listed as a valid UNDO command, it's possible that I may have tried to use it twice (instead of once) which caused the condition, but at any rate, beware of using CTRL+Z.

I am using the latest release, but have had this happen on older versions as well.