The issue is marshalling the JaxbHbmTuplizerType to xml. I know it is not a hibernate main feature and that's why I gave the lower priority. But as the JAXB bindings exist, let make them work... Might be very useful to generate mapping definition programmatically. I provided test cases with with the pull request that reproduce the problem. The simplest .hbm.xml that reproduces the problem is :
{{<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<hibernate-mapping xmlns="http://www.hibernate.org/xsd/orm/hbm">
<class>
<tuplizer class="org.hibernate.tuple.entity.DynamicMapEntityTuplizer"/>
<id/>
</class>
</hibernate-mapping>}}
This xml defines a valid mapping, but the generated binding cannot be reverted to xml (Try to marshall the generated JaxbHbmHibernateMapping back to xml).