Hibernate : 3.1.2
Hibernate Annotations: 3.1beta8
Hibernate EntityManager: 3.1beta6
Database: PostgreSQL 8.1.2

When invoking merge() for a detached object (see below) and another client was also updating the corresponding database record I receive an IllegalArgumentException. Optimistic synchronization is used via the @Version annotation.

MyPersistentClass detachedObj = ...
final EntityManager em = HibernateUtil.getEntityManager();
final EntityTransaction trans = em.getTransaction();
trans.begin();
detachedObj = em.merge(detachedObj);

Stack trace:
java.lang.IllegalArgumentException: org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [de.hska.kundenverwaltung.db.PrivatkundeEntity#<null>]
at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:141)
at de.hska.kundenverwaltung.db.KundenverwaltungDAO.updateKunden(KundenverwaltungDAO.java:155)
at de.hska.kundenverwaltung.Kundenverwaltung.editKunden(Kundenverwaltung.java:164)
at de.hska.kundenverwaltung.ui.EditKundenAction.execute(EditKundenAction.java:44)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:419)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:831)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:639)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1203)
at java.lang.Thread.run(Thread.java:595)

yes and?

The EJB Spec states on page 38 for the merge() method:
"IllegalArgumentException if instance is not an entity or is a removed entity"

In the case above the instance is a (detached) entity. In a concurrent transaction there was a "faster" modification.

Is it correct to throw an IllegalArgumentException ?

The next spec draft will introduce an OptimisticLockingException