Proxy classes appear to be a better way to implement the virtual classes created by annotations. This isn't a requirement of the spec and could possibly lower performance. There's more info in the new Classpath Sun compatibility file: http://cvs.savannah.gnu.org/viewcvs/classpath/sun/reflect/annotation/AnnotationInvocationHandler.java?rev=1.1.4.1&root=classpath&view=markup We should look into this as its highly likely we don't have correctly serializable annotations.