EclipseLinkJpaDialect applies per-transaction isolation level to shared DatabasePlatform

spring orm version: 5.1.4.RELEASE

In EclipseLinkJpaDialect class line 81

if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
	// Pass custom isolation level on to EclipseLink's DatabaseLogin configuration
	// (since Spring 4.1.2)
	UnitOfWork uow = entityManager.unwrap(UnitOfWork.class);
	uow.getLogin().setTransactionIsolation(definition.getIsolationLevel());
}

for instance:
If txA beginTransaction and there is Isolation.SERIALIZABLE around the repository class, the TransactionIsolation in uow.getLogin() will be changed to Isolation.SERIALIZABLE.
Then txB beginTransaction with Isolation.DEFAULT, the condition is not met, TransactionIsolation in uow.getLogin() still be SERIALIZABLE.

I think the right code should like this:

if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT
   && definition.getIsolationLevel() != entityManager.unwrap(UnitOfWork.class).getLogin().setTransactionIsolation()) {
	// ... 
}

Start in EclipseLinkJpaDialect around line 81 and trace how UnitOfWork and its shared DatabaseLogin hold transaction isolation. Reproduce the txA/txB sequence described in the issue, then inspect the relevant ORM tests or add coverage for custom isolation followed by ISOLATION_DEFAULT. Done means per-transaction isolation does not remain on the shared platform unexpectedly.