Cannot Marshal.dump jruby subclass of Java class

[headius]

From http://jira.codehaus.org/browse/JRUBY-6886

class Plain implements Serializable {
}

class D < Plain
end

Trying to Marshal.dump and instance of D results in the following error

TypeError: Java type is not serializable: org.jruby.javasupport.proxy.JavaProxyConstructor$2
  marshal_dump at org/jruby/java/proxies/JavaProxy.java:389
          dump at org/jruby/RubyMarshal.java:101
        (root) at marshal_derived.rb:16

Example java code and ruby code attached