Hibernate version: 3.1

Mapping documents:
<hibernate-mapping>
<class name="User" table="user">
<id name="id" column="user_id">
<generator class="Generator">
<param name="sequence_name">main_sequence</param>
</generator>
</id>
<property name="firstName" column="first_name"/>
....
<set name="emailAddresses" cascade="none">
<key column="user_id"/>
<one-to-many class="com.topcoder.web.reg.model.Email"/>
</set>
<joined-subclass name="BusinessUser" table="buser">
<key column="buser_id"/>
<property name="company"/>
</joined-subclass>
</class>
</hibernate-mapping>

<hibernate-mapping>
<class name="Email" table="email">
<id name="id" column="email_id">
<generator class="Generator">
<param name="sequence_name">EMAIL_SEQ</param>
</generator>
</id>
<property name="userId" column="user_id" access="field"/>
<property name="emailTypeId" column="email_type_id" access="field"/>
<property name="address" access="field"/>
<property name="primary" type="boolean" column="primary_ind" access="field"/>
<property name="statusId" column="status_id" access="field"/>
</class>
</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():
session.load(BusinessUser.class, id);

Name and version of the database you are using:
Informix 10.x

The generated SQL (show_sql=true):
Hibernate: select buser0_.buser_id as user1_9_0_, buser0_1_.first_name as first2_9_0_, buser0_1_.middle_name as middle3_9_0_, buser0_1_.last_name as last4_9_0_, buser0_1_.handle as handle9_0_, buser0_1_.status as status9_0_, buser0_1_.password as password9_0_, buser0_1_.activation_code as activation8_9_0_, buser0_.member_since as member2_12_0_, buser0_.quote as quote12_0_, buser0_.buser_type_id as buser4_12_0_, buser0_.comp_country_code as comp5_12_0_ from buser buser0_ inner join user buser0_1_ on buser0_.buser_id=buser0_1_.user_id where buser0_.buser_id=?
Hibernate: select emailaddre0_.user_id as user2_1_, emailaddre0_.email_id as email1_1_, emailaddre0_.email_id as email1_3_0_, emailaddre0_.user_id as user2_3_0_, emailaddre0_.email_type_id as email3_3_0_, emailaddre0_.address as address3_0_, emailaddre0_.primary_ind as primary5_3_0_, emailaddre0_.status_id as status6_3_0_ from email emailaddre0_ where emailaddre0_.user_id=?
Hibernate: update email set user_id=null where user_id=?
Hibernate: update email set user_id=? where email_id=?

This question I have is, why is hibernate performing those two updates on the email table? If I load the parent class (User), this does not happen. The data is loaded and there are no odd updates, however if I load the child class, this is what I get.

Any idea why?

Thanks