session.createCriteria(C1.class)
      .createCriteria("c2s", Criteria.LEFT_JOIN)
      .add(Restrictions.eq("PK", 2L))

create table t1 (pk number(15), cid number(15));
create table t2 (pk number(15), cid number(15), FK_T1 number(15));
insert into t1 values (1,1003);
insert into t2 values (1,1002,1);
insert into t2 values (2,1002,1);
insert into t2 values (3,1002,1);

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration SYSTEM "hibernate-configuration-3.0.dtd" >
<hibernate-configuration>
  <session-factory>
    <!-- Hibernate settings -->
     <property name="hibernate.dialect">org.hibernate.dialect.Oracle9iDialect</property>
     <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>

     <property name="hibernate.connection.pool_size">40</property>
     <property name="hibernate.connection.validationQuery">select 1 from dual</property>
     <property name="hibernate.connection.validationAttempts">5</property>
     <property name="hibernate.connection.validationAttemptTimeout">10</property>

      <property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1522:local11</property>
     <property name="hibernate.connection.username">hibernatetest</property>
     <property name="hibernate.connection.password">hibernatetest</property>
     
     <property name="hibernate.cache.provider_class">org.hibernate.cache.OSCacheProvider</property>
     <property name="hibernate.cache.use_query_cache">true</property>
     <property name="hibernate.format_sql">false</property>
     <property name="hibernate.show_sql">false</property>
  </session-factory>
</hibernate-configuration>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "hibernate-mapping-3.0.dtd" >
<hibernate-mapping auto-import="false">
  <class name="hibernatebug.C1" table="T1" discriminator-value="1003" batch-size="100" lazy="false" >
    <cache usage="read-write"/>
    <id name="PK" type="long" column="PK"/>
    <discriminator column="CID" type="long" insert="true"/>
   
    <bag name="c2s" lazy="extra" inverse="true" table="T2" optimistic-lock="false" >
      <cache usage="read-write"/>
      <key column="FK_T1" />
      <many-to-many class="hibernatebug.C2" column="PK"/>
    </bag>
   
  </class>
</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "hibernate-mapping-3.0.dtd" >
<hibernate-mapping auto-import="false">
  <class name="hibernatebug.C2" table="T2" discriminator-value="1002" batch-size="100" lazy="false" >
    <cache usage="read-write"/>
    <id name="PK" type="long" column="PK"/>
    <discriminator column="CID" type="long" insert="true"/>
  </class>
</hibernate-mapping>

package hibernatebug;

import java.util.List;

public class C1 {
   
   private Long pk;
   private Integer cid;
   private List<C2> fieldC2s;

   public Long getPK() {
      return pk;
   }

   public void setPK(Long pk) {
      this.pk = pk;
   }

   public Integer getCid() {
      return cid;
   }

   public void setCid(Integer cid) {
      this.cid = cid;
   }
   
   public List<C2> getC2s() {
        return this.fieldC2s;
    }
   
   public void setC2s(List<C2> newC2s) {
        this.fieldC2s = newC2s;
    }
   
}

package hibernatebug;

public class C2 {

   private Long pk;
   private Integer cid;

   public Long getPK() {
      return pk;
   }

   public void setPK(Long pk) {
      this.pk = pk;
   }

   public Integer getCid() {
      return cid;
   }

   public void setCid(Integer cid) {
      this.cid = cid;
   }
   
}

package hibernatebug;

import org.hibernate.Criteria;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.classic.Session;
import org.hibernate.criterion.Restrictions;

public class Test {

   public static void main(String[] args) {
      Configuration cfg = new Configuration();
      cfg.configure(Test.class.getClassLoader().getResource("hibernatebug/cfg.xml"));
      cfg.addClass(C1.class);
      cfg.addClass(C2.class);
      SessionFactory sf = cfg.buildSessionFactory();
      Session s = sf.openSession();
      
      C1 list = (C1) s.createCriteria(C1.class)
         .createCriteria("c2s", Criteria.LEFT_JOIN)
         .add(Restrictions.eq("PK", 2L))
         .uniqueResult();
      
      System.out.println("size of 'c2s' collection: " + list.getC2s().size() + " (expected 3)");
   }
   
}