Ahah actions causing form to corrupt

Ahah helper appears to cause drupal to lose all new form values below the last ahah action. For instance in this code. Filling all three fields out in order and then clicking submit causes a validation error that the last field is missing.

function application_form_page1($form_state) {
  ahah_helper_register($form, $form_state);

  $form['Name'] = array(
    '#type' => 'fieldset',
    '#title' => t('Name'),
    '#collapsible' => TRUE,
    '#collapsed' => FALSE,
  );
  $form['Name']['preferred'] = array(
    '#type' => 'textfield',
    '#title' => t('Preferred Name or Nickname'),
    '#default_value' => $form_state['values']['preferred'],
    '#description' => "The name you would like us to refer to you by. For example, <em>Bob</em> if your first name is <em>Robert</em>.",
    '#maxlength' => 20,
  '#size' => 20,
  );

// Birthplace Information
  $form['Birthplace_Information'] = array(
    '#type' => 'fieldset',
    '#title' => t('Birthplace Information'),
    '#prefix' => '<div id="birthplace-information-wrapper">', // This is our wrapper div.
    '#suffix' => '</div>',
    '#collapsible' => TRUE,
    '#collapsed' => FALSE,
  );
  $form['Birthplace_Information']['countryofbirth'] = array(
    '#type' => 'select',
    '#title' => t('Country of Birth'),
    '#default_value' => $form_state['values']['countryofbirth'],
    '#options' => array('' => '', 'a' => 'Somewhere', b => 'somewhere else'),
   '#ahah' => array(
     'path' => ahah_helper_path(array('Birthplace_Information')),
     'wrapper' => 'birthplace-information-wrapper',
     'method' => 'replace',
     'event' => 'change',
     'effect' => 'fade',
    ),
    '#required' => TRUE,
  );
  $form['Birthplace_Information']['update_countryofbirth'] = array(
    '#type' => 'submit',
    '#value' => t('Country of Birth'),
    '#submit' => array('ahah_helper_generic_submit'),
    '#attributes' => array('class' => 'no-js'),
  );

    $form['Birthplace_Information']['cityofbirth'] = array(
      '#type' => 'textfield',
      '#title' => t('City of Birth'),
      '#default_value' => $form_state['values']['cityofbirth'],
      '#required' => TRUE,
      '#maxlength' => 35,
      '#size' => 35,
    );
  $form['Submit'] = array(
  '#type' => 'submit',
  '#value' => t('Save and Continue'),
  );
  return ($form);

}