CDI interceptors are not called when invoking private observer method

The following code runs with an active transaction on WFLY 8.2.0, but failes with an TransactionRequiredException on WFLY 9.0.1:

@ApplicationScoped
public class InitCocktailDemoDataService
{
@PersistenceContext
private EntityManager entityManager;

@Transactional
private void createDemoData(@Observes @Initialized(ApplicationScoped.class) Object event)

It seems that interceptors aren't called at all - at least for observers of scope lifecycle events.