SwingBuilder edt breaks with anonymous subclassing

import groovy.swing.SwingBuilder
import javax.swing.SwingWorker;
import javax.swing.JFrame
import java.awt.BorderLayout

class TestEDT {
    public static void main( String[] args )
    {
        def myLabel
        def swing = new SwingBuilder()
        swing.edt {
            frame(pack:true, show:true, defaultCloseOperation:JFrame.EXIT_ON_CLOSE){
                borderLayout()
                myLabel = label("Hello", constraints:BorderLayout.CENTER)
            }

            def sw = new SwingWorker() {
                protected Object doInBackground() throws Exception
                {
                    return 10
                }
                protected void done()
                {
                    myLabel.text = get()
                }
            }.execute();
        }
    }
}

Exception in thread "main" groovy.lang.GroovyRuntimeException: Could not find matching constructor for: TestEDT$1(java.lang.Class, groovy.lang.Reference)
	at groovy.lang.MetaClassImpl.invokeConstructor(MetaClassImpl.java:1481)
	at groovy.lang.MetaClassImpl.invokeConstructor(MetaClassImpl.java:1397)
	at org.codehaus.groovy.runtime.callsite.MetaClassConstructorSite.callConstructor(MetaClassConstructorSite.java:46)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallConstructor(CallSiteArray.java:52)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:190)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:202)
	at TestEDT$_main_closure1.doCall(TestEDT.groovy:17)