Perhaps it simply means that they retain copyright in their portions, notthat they're stealing your derivative works. That would require a statement from the copyright holder before I'd belive it, though.
As you note, the "stealing your work" view requires some word-bending and would probably be invalid, so do we really *need* clarification?
Then again, someone may want to contact them about the aggressive tone in general anyway.
-- MJR/slef My Opinion Only and possibly not of any group I know. http://www.ttllp.co.uk/ for creative copyleft computing Help hack the EuroParl! http://mjr.towers.org.uk/proj/eurovote/