This appears to be a bug, or undocumented change in functionality. As
Keenle said in his comment, the temporarily answer can be found at
devforums.apple.com/message/1017433#1017433 in Post #7:
For NSDocumentClass, instead of just "ClassName" enter
"ModuleName.ClassName". The ModuleName being the main name of the module
(what you see at the top of the Project Navigtor and many other
So if your module was "MyProject" and your document was "MyDocument",
try entering "MyProject.MyDocument".