See also specification bug 6559178.

Also, it feels that the following (up)cast scenario should be flagged as
unchecked:

public class X<R> {
      static interface Interface extends Comparable<String> {}
      static final class Implements implements Interface {
            public int compareTo(String o) {
                  return 0;
            }
      }

      void method() {
            ((Comparable<R>) new Implements()).toString(); // unchecked ?
      }
}