<testsources> does not work with Ant groovyc task

Clover failed to integrate with <groovyc/>java.io.NotSerializableException: com.cenqua.clover.tasks.TestSourceSet
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1081)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:302)
        at java.util.ArrayList.writeObject(ArrayList.java:569)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:917)

... 

        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:302)
        at com.atlassian.clover.instr.java.InstrumentationConfig.saveToFile(InstrumentationConfig.java:427)
        at com.atlassian.clover.ant.groovy.GroovycSupport.newConfigDir(GroovycSupport.java:360)
        at com.atlassian.clover.ant.groovy.GroovycSupport.augmentCompilationClasspath(GroovycSupport.java:350)
        at com.atlassian.clover.ant.groovy.GroovycSupport.taskStarted(GroovycSupport.java:160)
        at org.apache.tools.ant.Project.fireTaskStarted(Project.java:2182)