I have the following data model class defined:
@PersistenceCapable
public class TestSerializableModelObj {
    @Persistent(serialized="true", defaultFetchGroup="true")
    private MyPOJO myField;
    @Persistent(serialized="true", defaultFetchGroup="true")
    private Collection<MyPOJO> myCollection;
    // getter/setters
}
MyPOJO is just a simple class that implements Serializable.
When I persist this via DataNucleus/JDO and retrieve it I can read myField just fine, but myCollection is null (though I set it to be an Vector of two MyPOJO objects before persisting it).