Hibernate 3.1, Jboss 4.0.3SP1

I'm trying to get optimistic locking to work, but with no luck.

I'm using Jboss cache 1.4. Configuration of cache and session factory:

<server>
 <mbean code="org.jboss.cache.TreeCache" name="jboss.har:service=HarSecondLevelCache">
 <attribute name="CacheMode">LOCAL</attribute>
 <attribute name="TransactionManagerLookupClass">org.jboss.cache.JBossTransactionManagerLookup</attribute>
 <attribute name="NodeLockingScheme">OPTIMISTIC</attribute>
 <attribute name="EvictionPolicyConfig">
 <config>
 <attribute name="wakeUpIntervalSeconds">5</attribute>
 <!-- Cache wide default -->
 <region name="/_default_">
 <attribute name="maxNodes">50000</attribute>
 <attribute name="timeToLiveSeconds">1000</attribute>
 <!-- Maximum time an object is kept in cache regardless of idle time -->
 <attribute name="maxAgeSeconds">600</attribute>
 </region>
 </config>
 </attribute>
 </mbean>
 <mbean code="org.jboss.hibernate.jmx.Hibernate" name="jboss.har:service=Chip_HB_LOCAL">
 <attribute name="DatasourceName">java:/jdbc/ChipDS_LOCAL</attribute>
 <attribute name="Dialect">org.hibernate.dialect.PostgreSQLDialect</attribute>
 <attribute name="SessionFactoryName">java:/hibernate/ChipHB_LOCAL</attribute>
 <attribute name="CacheProviderClass">org.jboss.hibernate.cache.DeployedTreeCacheProvider</attribute>
 <attribute name="DeployedTreeCacheObjectName">jboss.har:service=HarSecondLevelCache</attribute>
 <attribute name="ReflectionOptimizationEnabled">false</attribute>
 <attribute name="MaxFetchDepth">1</attribute>
 <attribute name="ScanForMappingsEnabled">true</attribute>
 <attribute name="StatGenerationEnabled">true</attribute>
 <attribute name="ShowSqlEnabled">false</attribute>
 <!--attribute name="Hbm2ddlAuto">update</attribute-->
 </mbean>
</server>

Here is my class that I expect to be optimistically locked:

/*
 * $Id$
 */
package hr.chipoteka.erp.data;

import java.util.Date;

/**
 * @hibernate.class lazy = "false" dynamic-update = "true"
 */
public abstract class Analitika extends DataObject {
...

 /**
 * @hibernate.version type = "timestamp"
 */
 public Date getTs() {
 return ts;
 }

 public void setTs(Date ts) {
 this.ts = ts;
 }
}

and one subclass:

package hr.chipoteka.erp.data.artikl;

import hr.chipoteka.erp.data.Analitika;
import hr.chipoteka.erp.data.SlimDataObject;
import hr.chipoteka.erp.data.osoba.PoslovniPartner;
import hr.chipoteka.erp.data.osoba.adresa.Drzava;

import java.util.*;

/**
 * @hibernate.union-subclass lazy = "false" dynamic-update = "true"
 */
public class Artikl extends Analitika implements SlimDataObject {
...
}

Generated hbm.xml looks like this:

?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
 "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping

>

 <class
 name="hr.chipoteka.erp.data.Analitika"
 lazy="false"
 dynamic-update="true"
 >

...

 <version
 name="ts"
 column="ts"
 type="timestamp"
 />

...

 <union-subclass
 name="hr.chipoteka.erp.data.artikl.Artikl"
 dynamic-update="true"
 lazy="false"
 >

...

 </union-subclass>
...
 </class>

</hibernate-mapping>

I use hibernate within stateless session beans.

When running some HQL queries, I stop jboss at a breakpoint and check locks in the database (postgres):

select pg_class.relname,pg_locks.locktype, page, tuple, transaction, pid, mode, granted from pg_class,pg_locks where pg_class.relfilenode=pg_locks.relation and pid = 31761 order by relname;
 relname | locktype | page | tuple | transaction | pid | mode | granted
---------------+----------+------+-------+-------------+-------+-----------------+---------
 artikl | relation | | | 5378326 | 31761 | AccessShareLock | t
(1 rows)

What am I doing wrong?