Symfony2: event-listener inside subform never called / event not dispatched

I have a form type that includes another type of form.

I have added event-listener to the subform, but the listener is never executed.

The first type of form:

class AFormType extends AbstractType {

   public function buildForm(FormBuilderInterface $builder, array $options) {
       $builder
               ->add('aSubFormType', new SubFormType());
   }
//[...]
}

The second type of form:

class SubFormType extends AbstractType
{

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
    $builder->add("metier", "text");

    $builder->addEventListener(
        \Symfony\Component\Form\FormEvents::PRE_SET_DATA,
        function(\Symfony\Component\Form\FormEvent $event){
        // Some Stuff never executed
    });        
    }
}

I do not know if this behavior is correct or is it a mistake? And how can I use EventListner in a sub form?

thank