I'm the author of Zotero Better BibTeX; my extension generates BibTeX including a JabRef groupstree that is intended to import cleanly into JabRef. Recenty I've had reports that this import fails; this means my implementation of the groupstree is faulty, but as I cannot find any documentation on the format, I don't know in what way it is faulty.

I have a sample at https://drive.google.com/open?id=0BxFpK0V-elKWSVE1ejdLVkdiNXc, if someone could have a look at what I did wrong it'd be hugely appreciated. The BBT-generated groupstree is very simple and always only has ExplicitGroup entries.