<class name="ServiceLevel" table="servicelevel">
      <id name="id" column="servicelevel_id" type="long" unsaved-value="null">
         <generator class="sequence">
            <param name="sequence">servicelevel_sequence</param>
         </generator>
      </id>
      <discriminator column="type"/>

      <property name="name" column="name"/>

      <subclass name="BaseServiceLevel" discriminator-value="0"/>
      <subclass name="Accessorial" discriminator-value="1"/>
   </class>

   <class name="ServiceGroup" table="servicegroup">
      <id name="id" column="servicegroup_id" type="long" unsaved-value="null">
         <generator class="sequence">
            <param name="sequence">servicegroup_sequence</param>
         </generator>
      </id>
      <property name="name" column="name"/>

      <set name="baseServices" table="servicegroup_content" lazy="true">
         <key column="servicegroup_id"/>
         <many-to-many column="servicelevel_id" class="BaseServiceLevel"/>
      </set>
      <set name="accessorials" table="servicegroup_content" lazy="true" >
         <key column="servicegroup_id"  />
         <many-to-many column="servicelevel_id" class="Accessorial"/>
      </set>
   </class>

Hibernate: select servicegro0_.servicegroup_id as serviceg1_0_, servicegro0_.name as name0_ from servicegroup servicegro0_ where servicegro0_.servicegroup_id=?
Hibernate: select baseservic0_.servicegroup_id as serviceg1___, baseservic0_.servicelevel_id as servicel2___, baseservic1_.servicelevel_id as servicel1_0_, baseservic1_.name as name0_, baseservic1_.abbreviation as abbrevia4_0_, baseservic1_.price_unit as price_unit0_ from servicegroup_content baseservic0_, servicelevel baseservic1_ where baseservic0_.servicegroup_id=? and baseservic0_.servicelevel_id=baseservic1_.servicelevel_id
Hibernate: select accessoria0_.servicegroup_id as serviceg1___, accessoria0_.servicelevel_id as servicel2___, accessoria1_.servicelevel_id as servicel1_0_, accessoria1_.name as name0_, accessoria1_.abbreviation as abbrevia4_0_, accessoria1_.price_unit as price_unit0_ from servicegroup_content accessoria0_, servicelevel accessoria1_ where accessoria0_.servicegroup_id=? and accessoria0_.servicelevel_id=accessoria1_.servicelevel_id

   <class name="ServiceLevel" table="servicelevel">
      <id name="id" column="servicelevel_id" type="long" unsaved-value="null">
         <generator class="sequence">
            <param name="sequence">servicelevel_sequence</param>
         </generator>
      </id>
      <discriminator column="type"/>

      <property name="name" column="name"/>

      <subclass name="BaseServiceLevel" discriminator-value="0"/>
      <subclass name="Accessorial" discriminator-value="1"/>
   </class>

<class name="Engagement" table="engagement" lazy="false">
   <id name="id" column="engagement_id" type="long" unsaved-value="null">
      <generator class="sequence">
         <param name="sequence">engagement_sequence</param>
      </generator>
   </id>

   <property name="name" column="name"/>

   <set name="baseServiceLevels" inverse="true" lazy="true" table="servicelevel" cascade="all-delete-orphan">
      <key column="engagement_id"/>
      <one-to-many class="BaseServiceLevel"/>
   </set>
   <set name="accessorials" inverse="true" lazy="true" table="servicelevel" cascade="all-delete-orphan">
      <key column="engagement_id"/>
      <one-to-many class="Accessorial"/>
   </set>
</class>

      Engagement e = engagementDao.getEngagement(new Long(-1000));
      Set baseServices = e.getBaseServiceLevels();
      Set accessorials = e.getAccessorials();
      for (Iterator iterator = baseServices.iterator(); iterator.hasNext();)
      {
         Object o = (Object) iterator.next();
         System.out.println(o);
      }
      for (Iterator iterator = accessorials.iterator(); iterator.hasNext();)
      {
         Object o = (Object) iterator.next();
         System.out.println(o);
      }

org.hibernate.WrongClassException: Object with id: -1011 was not of the specified subclass: Accessorial (loaded object was of wrong class)
   at org.hibernate.loader.Loader.instanceAlreadyLoaded(Loader.java:824)
   at org.hibernate.loader.Loader.getRow(Loader.java:780)
   at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:295)
   at org.hibernate.loader.Loader.doQuery(Loader.java:389)
   at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:208)
   at org.hibernate.loader.Loader.loadCollection(Loader.java:1367)
   at org.hibernate.loader.collection.OneToManyLoader.initialize(OneToManyLoader.java:107)
   at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:488)
   at org.hibernate.event.def.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:60)
   at org.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:1356)
   at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:171)
   at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:48)
   at org.hibernate.collection.PersistentSet.iterator(PersistentSet.java:134)
   at EngagementDAOTestCase.testEngagement2(EngagementDAOTestCase.java:68)

select baseservic0_.engagement_id as engagement6___, baseservic0_.servicelevel_id as servicel1___, baseservic0_.servicelevel_id as servicel1_7_, baseservic0_.name as name16_7_,  baseservic0_.engagement_id as engagement6_16_7_,  engagement2_.engagement_id as engagement1_1_, engagement2_.name as name3_1_,  from servicelevel baseservic0_, engagement engagement2_, where baseservic0_.engagement_id=?

select accessoria0_.engagement_id as engagement6___, accessoria0_.servicelevel_id as servicel1___, accessoria0_.servicelevel_id as servicel1_7_, accessoria0_.name as name16_7_,  accessoria0_.engagement_id as engagement6_16_7_,  engagement2_.engagement_id as engagement1_1_, engagement2_.name as name3_1_,  from servicelevel accessoria0_, engagement engagement2_, where accessoria0_.engagement_id=?