Your mapping is IMO still invalid, it might have worked before due to a flaw. The one to one implementation of 5.3 was definitely flawed. We solved a couple of bugs. One of which where the parent side of the one to one association was actually treated as child.

I wouldn’t classify this issue as a bug personally until we have shown that the issue persists after fixing the mapping. That means that the identifier of your child side of the association should be persistable/insertable.

Please consider writing a test case based on the Hibernate test case template so we can play around with the model and see what needs to be fixed.