Bill, I agree, the issue with cc0/PDDL is about avoiding doubt though. Where the intent is clear to a "reasonable" person then I think you'd probably survive on that in court. Here the main point for me was that the authors said something that I would have intepreted as carte blanche but clearly in their own minds didn't mean that. So whatever the legal status might be the end result was confusion.

Mr Gunn, I thought you had defended? Now I'll need to go back and edit the post...