The thread on the dev list is "Does this seem like a compiler bug?".
Jason pointed to this bug which seems to capture the problem:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6557279
The generics tutorial talks about Collection(?) being "...
(pronounced “collection of unknown�) , that is, a collection whose element type matches
anything.", so I don't see how Collection(Class(?)) can be interpreted as a collection of a single type of class.