The folks at Mindola have been very responsive, and they may have found the problem -- it may have to do with hitting cmd-X in a certain view. (I did not intentionally do this but it is possible I might have bumped the keys -- I am a big klutz on my iBook's little keyboard). Of course it did not do what would have been expected, as the deck disappeared from the Explorer while still remaining in the main window, so I didn't automatically guess what the problem might have been.

Thanks to Mindola for working on this.

It's still a good idea to always back-up your work, no matter what program you are using. ;)