JAXB marshaller exception - bound to an anonymous type

I'm trying to write a program that can programmatically assemble a FOP document, for generation of a PDF. I know, reinventing the wheel, but I'm just doing it as an excercise.

I've obtained the XSD for FOP from here: http://ift.tt/1v0hUAf

I used that with XJC to generate JAXB objects, and I'm composing a document as follows:

public static void main(String[] args) throws Exception {

    JAXBContext jaxbContext = JAXBContext.newInstance(Root.class);
    Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
    jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

    Root root = new Root();
    LayoutMasterSet layoutMasterSet = new LayoutMasterSet();
    SimplePageMaster simplePageMaster = new SimplePageMaster();
    simplePageMaster.setMasterName("one");
    RegionBody regionBody = new RegionBody();
    simplePageMaster.setRegionBody(regionBody);
    layoutMasterSet.getSimplePageMasterOrPageSequenceMaster().add( simplePageMaster );

    PageSequence pageSequence = new PageSequence();
    pageSequence.setMasterReference("one");
    Flow flow = new Flow();
    flow.setFlowName("xsl-region-body");
    pageSequence.setFlow(flow);
    layoutMasterSet.getSimplePageMasterOrPageSequenceMaster().add(pageSequence);
    root.setLayoutMasterSet( layoutMasterSet );

    jaxbMarshaller.marshal(root, System.out);

}

This code works fine until I include the part that adds the PageSequence -

then it throws the following exception:

 Exception in thread "main" javax.xml.bind.MarshalException
- with linked exception:
[com.sun.istack.internal.SAXException2: Instance of "com.company.jaxb.fop.PageSequence" is substituting "java.lang.Object", but "com.company.jaxb.fop.PageSequence" is bound to an anonymous type.]
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:311)
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:236)
at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:95)
at FopTry.main(FopTry.java:43)
Caused by: com.sun.istack.internal.SAXException2: Instance of "com.company.jaxb.fop.PageSequence" is substituting "java.lang.Object", but "com.company.jaxb.fop.PageSequence" is bound to an anonymous type.
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:237)
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:652)

Any ideas what's going wrong?