Specifying default implementation for polymorphic enums doesn't work

I have an interface implemented by a couple of enum classes and I am trying to setup one of them as the default implementation for that interface using XStream.addDefaultImplementation(). This doesn't however prevent the class attribute from getting encoded into XML. After discussing the problem in the user mailing list, Jorg suggested that it should be a bug. I will try to create and attach a unit test to make fixing this issue easier, but for reference, here is the thread where this discussion happened:

http://article.gmane.org/gmane.comp.java.xstream.user/4222