Calling CMT bean from BMT bean results in "Local transaction already has 1 non-XA Resource" - jpa-2.0

Question

I have one EJB with Bean-Managed transaction:
#Singleton
#TransactionManagement(TransactionManagementType.BEAN)
public class BmtBean {
#Resource
private DataSource ds1;
#Resource
private SessionContext sessionCtx;
#EJB
private CmtBean cmtBean;
public void callCmtBean() {
Connection conn1 = null;
try {
conn1 = ds1.getConnection();
// create a PreparedStatement and execute a query
// process result set
while(resultSet.next()) {
// map resultSet to an entity
Entity entity = mapResultSetToEntity(resultSet);
sessionCtx.getUserTransaction().begin();
// pass an entity to another EJB,
// that operates on a different JTA data source
cmtBean.call(entity);
sessionCtx.getUserTransaction().commit();
}
} finally {
// release connection
}
}
}
And another bean with container-managed transaction:
#Singleton
#TransactionManagement(TransactionManagementType.CONTAINER)
public class CmtBean {
#PersistenceContext
private EntityManager em;
#TransactionAttribute(TransactionAttributeType.MANDATORY)
public void call(Entity entities) {
//persist passed entities
//em.flush()
//em.clear();
}
}
Calling cmtBean#call doesn't cause TransactionRequiredException, because prior to that I start a UserTransaction. But when em#flush is called, this exception is thrown:
Caused by: javax.resource.spi.ResourceAllocationException: Error in
allocating a connection. Cause: java.lang.IllegalStateException: Local
transaction already has 1 non-XA Resource: cannot add more resources.
After digging some EclipseLink code, I see that when calling em#flush() it attempts to obtain a new connection from dataSource and fails to do so.
Is this a bug or expected behaviour? How can I fix this?
UPDATE:
See the updated code example.
Also, I have to stress, that I do use 2 non-XA JTA data sources. But since the connection in BmtBean is by default set to autocommit, by the time CmtBean is called, the transaction has to be already commited.