transaction-blueprint Coordinations should check existing TX

I have this unannotated method:

transactionManager.begin();
try {
	nestedTestService.testExternalTransaction();
} finally {
	transactionManager.rollback();
}

And this annotated nestedTestService.testExternalTransaction():

@Transactional(TxType.REQUIRED)
public void testExternalTransaction() {
	TestEntity testEntity = testDao.createNew();
...

While the dao uses this EntityManager with the support from <jpa:enable />:

@PersistenceContext(unitName = "unit.1")
private EntityManager entityManager;

The problem is that after ARIES-2050 fixes, org.apache.aries.transaction.TxInterceptorImpl#preCall() is not blindly creating new coordination if there's existing transaction.
ARIES-2050 fix was not complete (see also ARIES-2073) but also I've mishandled the scenario where transaction is created not by another TxInterceptorImpl.preCall(), but by manual javax.transaction.TransactionManager#begin() invocation.