I have old .hbm.xml files with a map defined <map name="traductions" sort="natural" >. The POJO has a SortedMap. It works great with Hibernate 4.3.10.Final.
When I migrate to Hibernate 5.1.0.Final, it doesn't work anymore. I trace the problem in PluralAttributeSourceMapImpl that doesn't implements org.hibernate.boot.model.source.spi.Sortable. The only class that implements Sortable is PluralAttributeSourceSetImpl. So I guess SortedSet are managed, but not SortedMap.