BibDesk does not permit parentheses within the Cite Key field even though BibTeX works perfectly well with such parentheses and other BibTeX database programs (such as JabRef) permit it. So I think this qualifies it as a bug in BibDesk.
Question: Until this is fixed, is there a workaround for using BibDesk on an already constructed BibTeX databases that includes parentheses in the Cite Key field without having to change all the entries and \cite commands in documents that use such entries?