Hibernate version: 3.1.3

Full stack trace of any exception that occurs:
Exception in thread "main" java.lang.ClassCastException: com.example.MyPersistentBag cannot be cast to org.dom4j.Element
at org.hibernate.type.CollectionType.setToXMLNode(CollectionType.java:552)
at org.hibernate.property.Dom4jAccessor$ElementSetter.set(Dom4jAccessor.java:310)
at org.hibernate.tuple.AbstractEntityTuplizer.setPropertyValues(AbstractEntityTuplizer.java:330)
at org.hibernate.persister.entity.AbstractEntityPersister.setPropertyValues(AbstractEntityPersister.java:3232)
at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:129)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:842)
at org.hibernate.loader.Loader.doQuery(Loader.java:717)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
at org.hibernate.loader.Loader.loadCollection(Loader.java:1919)
at org.hibernate.loader.collection.CollectionLoader.initialize(CollectionLoader.java:36)
at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:520)
at org.hibernate.event.def.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:60)
at org.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:1676)
at org.hibernate.type.CollectionType.getCollection(CollectionType.java:507)
at org.hibernate.type.CollectionType.resolveKey(CollectionType.java:341)
at org.hibernate.type.CollectionType.resolve(CollectionType.java:335)
at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:116)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:842)
at org.hibernate.loader.Loader.doQuery(Loader.java:717)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
at org.hibernate.loader.Loader.doList(Loader.java:2145)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
at org.hibernate.loader.Loader.list(Loader.java:2024)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:94)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1533)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:283)
at <my code>


It seems like built-in collection types have special handling for use within dom4j but I can't see how to integrate a user collection type for use with the dom4j entity mode. Is this even possible?