JPA persist , detach, merge creates two records in DB when executed in the same transaction in JBoss

Issue

We are having problems using JPA in CMT.

Transaction is started from an EJB, and the following code is called to persist records:

EntityManager em = factory.createEntityManager();
try {
     if (serviceRequest.getDbId() == null){
         em.persist(serviceRequest);
     } else {
         em.merge(serviceRequest);
     }
} 
finally {
     em.close();
}

The code is called twice, the first time with a new object, which will execute "em.persist(serviceRequest);", and then a second time after the serviceRequest object is modified, which will execute "em.merge(serviceRequest);". Both these calls are in the same JTA transaction.
The result is that there are 2 records created in the DB, both containing the modified serverRequest. I was expecting only one record.

I attach the datasource and persistence.xml used.

EntityManager is created programmatically in the DAO like this:

entityManagerProps = new HashMap<String, String>();
entityManagerProps.put("hibernate.connection.datasource", "java:TestDS");
entityManagerProps.put("hibernate.default_schema", "TestDSSchema");
factory = Persistence.createEntityManagerFactory("TestPersist", entityManagerProps);