Hi @Guillaume Smet my bad - I reworked the example by adding a mapped superclass and it still breaks. I believe it's a bug - check my test-case https://github.com/ptahchiev/hibernate-test-case-templates/tree/HHH-12609 and you will see in the log there is both constraints added for Taxon:
Hibernate: alter table taxon add constraint UKcqy7383ll4wy6b9efu96s20o7 unique (catalog_version_id, code) Hibernate: alter table taxon add constraint UK_ko1v2asmbj5kfeapum261i6c7 unique (code)