StaleObjectStateException with processes which have Rule Tasks in jBPM5

Issue

• I have multiple threads which take care of its own ksession and process instance. So I expect that process instances are isolated. But StaleObjectStateException occurs if processes have Rule Tasks.

ERROR [org.hibernate.event.def.AbstractFlushingEventListener] (http-0.0.0.0-8080-5) Could not synchronize database state with session
org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [org.jbpm.persistence.processinstance.ProcessInstanceInfo#8]
        at org.hibernate.persister.entity.AbstractEntityPersister.check(AbstractEntityPersister.java:1782)
        at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2425)
        at org.hibernate.persister.entity.AbstractEntityPersister.updateOrInsert(AbstractEntityPersister.java:2325)
        at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2625)
        at org.hibernate.action.EntityUpdateAction.execute(EntityUpdateAction.java:115)
        at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:278)
        at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:262)
        at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:167)
        at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
        at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
        at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1030)
        at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:367)
        at org.hibernate.ejb.AbstractEntityManagerImpl$1.beforeCompletion(AbstractEntityManagerImpl.java:504)
        at com.arjuna.ats.internal.jta.resources.arjunacore.SynchronizationImple.beforeCompletion(SynchronizationImple.java:101)
        at com.arjuna.ats.arjuna.coordinator.TwoPhaseCoordinator.beforeCompletion(TwoPhaseCoordinator.java:272)
        at com.arjuna.ats.arjuna.coordinator.TwoPhaseCoordinator.end(TwoPhaseCoordinator.java:89)
        at com.arjuna.ats.arjuna.AtomicAction.commit(AtomicAction.java:160)
        at com.arjuna.ats.internal.jta.transaction.arjunacore.TransactionImple.commitAndDisassociate(TransactionImple.java:1433)
        at com.arjuna.ats.internal.jta.transaction.arjunacore.BaseTransaction.commit(BaseTransaction.java:137)
        at com.arjuna.ats.jbossatx.BaseTransactionManagerDelegate.commit(BaseTransactionManagerDelegate.java:75)
        at org.jboss.tm.usertx.client.ServerVMClientUserTransaction.commit(ServerVMClientUserTransaction.java:162)
        at org.drools.persistence.jta.JtaTransactionManager.commit(JtaTransactionManager.java:179)
        at org.drools.persistence.SingleSessionCommandService.execute(SingleSessionCommandService.java:359)
        at org.drools.command.impl.CommandBasedStatefulKnowledgeSession.fireAllRules(CommandBasedStatefulKnowledgeSession.java:249)