Trying to understand this better here, Spring docs suggest that the EntityManager injected by @PersistenceContext is actually a Shared Entity Manager which can be shared among multiple threads, which actually makes me now believe that this is not a Hibernate bug but rather a Spring bug. I was already aware that the Session/EntityManager is not thread-safe, but i forgot the fact that even though the provider is Hibernate here, the EntityManager instance is controlled/injected by Spring. Will raise a corresponding bug with Spring then. Thanks a lot for the quick turn-around Brett.