class HydrationListener extends Doctrine_Record_Listener
{
    public function preHydrate(Doctrine_Event $event)
    {
        $data['fullname'] = $data['fname'] . ' ' . $data['name'];
        $event->data = $data;
    }
}

When you dump your data, you get :

User:
  User_1:
    name: Doe
    fname: John
    fullname: John Doe

But, If you reload the fixture, you get the error that it doesn't know the component 'fullname'. The dump must not generate the 'fullname' in the fixture