Hibernate "IllegalStateException: An entity copy was already assigned to a different entity" in JBoss EAP 6

Issue

Migrating to EAP 6/Hibernate 4 and encountering an exception like the following

ERROR [org.jboss.as.ejb3.invocation] (http-/0.0.0.0:443-1) JBAS014134: EJB Invocation failed on component SatelliteDao for method public abstract long com.xzy.Dao.persist(com.xyz.SomeEntity) throws java.lang.IllegalStateException: An entity copy was already assigned to a different entity.
    at org.jboss.as.ejb3.tx.CMTTxInterceptor.handleExceptionInOurTx(CMTTxInterceptor.java:165) [jboss-as-ejb3-7.1.2.Final-redhat-1.jar:7.1.2.Final-redhat-1]
...
Caused by: java.lang.IllegalStateException: An entity copy was already assigned to a different entity.
    at org.hibernate.event.internal.EventCache.put(EventCache.java:184) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
    at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:285) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]
    at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151) [hibernate-core-4.1.3.Final-redhat-1.jar:4.1.3.Final-redhat-1]