Hibernate version:3.1.2
Name and version of the database you are using:Sybase ASE 12.5.2
The generated SQL (show_sql=true):
------------
I have such mapping:

<class name="NodeElement" table="nodes_elements">
<id name="id">
<generator class="native" />
...
</id>
<joined-subclass name="Page" extends="NodeElement" table="pages">
<key column="node_element_id" />
...
</joined-subclass>

<!-- more joined sublasses -->

</class>

In code, when I create Page object, it is saved OK, but
when I read Page object ( it is readed fine ) instanceof Page returns false
and page.getClass().getName() returns xxx.NodeElement$$EnhancerByCGLIB$$1f06513e.

How can I test which of joined subclasses I have?

The problme was not in subclass mapping, but in using of it.
Thats how property using my NodeElement was mapped:
<many-to-one name="nodeElement" column="node_element_id" not-null="false" />
and the only thing I added was fetch="join" and thats all! problem solved.
Sorry for panic. :)