Detached entity cannot be merged via cascade merge in JBoss EAP 6

Issue

• Migrating Hibernate 3 application to Hibernate 4
• EntityA has two CascadeType.MERGE associations to EntityB: relatedB1 and relatedB2
• An instance of EntityB is instantiated, persisted, detached then associated with EntityA via relatedB1
• The persisted instance of EntityB is loaded by a query and associated with EntityA via relatedB2
• When EntityA is merged to the data store, an exception like the following is raised:

java.lang.IllegalStateException: Error occurred while storing entity [test.EntityB@20]. An entity copy [test.EntityB#1] was already assigned to a different entity [test.EntityB@20].
    at org.hibernate.event.internal.EventCache.put(EventCache.java:192)
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:285)
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
    ...
    at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:902)
    at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:889)
    ...