Item item = em.getReference(Item.class, 123);
em.remove(item);
em.persist(item);

main            ] ERROR  - 12:51:21,920 - org.hibernate.AssertionFailure: HHH000099: an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session): org.hibernate.AssertionFailure: Unable to perform un-delete for instance org.jpwh.model.simple.Item
org.hibernate.AssertionFailure: Unable to perform un-delete for instance org.jpwh.model.simple.Item
	at org.hibernate.engine.spi.ActionQueue.unScheduleDeletion(ActionQueue.java:527)
	at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:158)
	at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:79)
	at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:854)
	at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:828)
	at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:832)
	at org.hibernate.jpa.spi.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:1022)

Caused by: org.hibernate.HibernateException: identifier of an instance of org.jpwh.model.simple.Item was altered from 1000 to null
	at org.hibernate.event.internal.DefaultFlushEntityEventListener.checkId(DefaultFlushEntityEventListener.java:82)
	at org.hibernate.event.internal.DefaultFlushEntityEventListener.getValues(DefaultFlushEntityEventListener.java:194)
	at org.hibernate.event.internal.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:156)
	at org.hibernate.event.internal.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:229)
	at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:102)
	at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
	at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1235)
	at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:405)