As I mentioned in the Hibernate dev mailing list. I think the spec says that a provider must include META-INF/orm.xml by default. The fact that the PersistenceUnit implementor is adding it is the reason for the failure.

We could try and be nice a detect that someone tries to add the file in parallel but we haven't guarded against PersistenceUnit implementor fuzzy behaviors as there is so few of them in existence.