Filefield incompatibility

Hi:
My form was working ok until I added a filefield. Now the AHAH is not working properly.
The filefield module somehow alters the $form_state object and values are lost.
More specifically:
Here´s a select box that triggers ahah and thus a form change:

$form['etiquetas']['tectag_1'] = array(
      '#type' => 'select',
      '#title' => t('Tag'),
	  '#size' => 1,
	  '#options'=>makePrimaryTree($form,$form_state),
	  '#prefix' => '<div id="tagwrapper-'. $i.'">',
      '#suffix' => '</div>',
      '#default_value' => $form_state['values']['etiquetas']['tectag_'. $i],
	  '#multiple' => false,
		  '#ahah' => array(
		  'event' => 'change', // When the button is "clicked", AHAH will do it's job
		  'path' => ahah_helper_path(array('etiquetas')),
		  'wrapper' => 'etiquetas-wrapper', // We then define the wrapper which will be changed.
		),
    );

Ok, so that runs the form_alter function on the event 'change'.
Without the filefield module:
drupal_set_message('

Form state here:'. print_r($form_state['etiquetas']['values'], TRUE) .'

');
Will output:

 [etiquetas] => Array
                (
                    [tectag_1] => 29
                    [add_more] => Agrerar Campo Tecnología
                )

But with the filefield module on the form it is:

 [etiquetas] => Array
                (
                    [tectag_1] =>
                    [add_more] => Agrerar Campo Tecnología
                )

So it´s not getting the actual selected value and thus I can´t go any further.
Hope it´s clear enough and that someone can help.

Thanks in advance