Description of problem:

According to JPA 2.1, section 3.2.4 (Synchronization to the Database)

"The semantics of the flush operation, applied to an entity X are as follows:
...
• For any entity Y referenced by a relationship from X, where the relationship to Y has not been annotated with the cascade
element value cascade=PERSIST or cascade=ALL
• If Y is new or removed, an IllegalStateException will be thrown
by the flush operation (and the transaction marked for rollback) or the transaction commit will fail."

Prior to fixing HHH-9330, EntityManager operated properly when the relationship to Y is one-to-one. After HHH-9330 was fixed, IllegalStateException is no longer thrown when Y is new.

https://hibernate.atlassian.net/browse/HHH-9568

How reproducible: always

Steps to Reproduce:
See org.hibernate.jpa.test.cascade.CascadeTest.testFlushTransientOneToOne().

Actual results:
IllegalStateException is no longer thrown when Y is new.

Expected results:
An IllegalStateException will be thrown
by the flush operation (and the transaction marked for rollback) or the transaction commit will fail

Additional info:
This fix reverts https://bugzilla.redhat.com/show_bug.cgi?id=1182303 (https://hibernate.atlassian.net/browse/HHH-9330).