hibernate-mapping-3.0.dtd does not allow for a composite-id element to have a nested tuplizer element.

However, composite-ids are otherwise treated as components, which makes me think that the dtd looks to be inconsistent with the general design in that respect. In fact, it is. Modifying the composite-id element declaration on the dtd to allow for tuplizer elements leads to a perfectly expected behavior: The registered tuplizer class gets instantiated and used upon the creation of the composite-id instance.