Issue

• jBPM5 を使いビジネスプロセスを作成しました。フローを数回処理すると、フローは以下の ERROR メッセージを表示します。
  実行環境ですが、WebSphere Application Server (WAS) 8 で、 JBoss Enterprise BRMS Platform 5.3 に同梱される jBPM 5.x を使用しています。
  この ERROR メッセージが表示される理由は?

java.lang.RuntimeException:Could not commit transaction
    at org.jbpm.task.service.TaskServiceSession.doOperationInTransaction(TaskServiceSession.java:1011)
    at org.jbpm.task.service.TaskServiceSession.getContent(TaskServiceSession.java:589)
    at org.jbpm.task.service.local.LocalTaskService.getContent(LocalTaskService.java:130)
    at org.jbpm.process.workitem.wsht.SyncWSHumanTaskHandler$TaskCompletedHandler.handleCompletedTask(SyncWSHumanTaskHandler.java:343)
        .....
Caused by: java.lang.RuntimeException:Unable to commit transaction
    at org.drools.persistence.jta.JtaTransactionManager.commit(JtaTransactionManager.java:182)
    at org.jbpm.task.service.persistence.TaskJTATransactionManager.commit(TaskJTATransactionManager.java:56)
    at org.jbpm.task.service.persistence.TaskPersistenceManager.endTransaction(TaskPersistenceManager.java:94)
    at org.jbpm.task.service.TaskServiceSession.doOperationInTransaction(TaskServiceSession.java:999)
        .....
Caused by: javax.transaction.RollbackException
    at com.ibm.tx.jta.impl.TransactionImpl.stage3CommitProcessing(TransactionImpl.java:1258)
    at com.ibm.tx.jta.impl.TransactionImpl.processCommit(TransactionImpl.java:1028)
    at com.ibm.tx.jta.impl.TransactionImpl.commit(TransactionImpl.java:949)
        .....
Caused by: javax.persistence.OptimisticLockException
    at org.hibernate.ejb.AbstractEntityManagerImpl.wrapStaleStateException(AbstractEntityManagerImpl.java:627)
    at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:588)
    at org.hibernate.ejb.AbstractEntityManagerImpl$1.beforeCompletion(AbstractEntityManagerImpl.java:513)
        .....    
Caused by: org.hibernate.StaleObjectStateException:Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect):[org.jbpm.task.Task#5]
    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:279)
        .....