Added form element appends unwanted to pager url

Hi there....

Can anyone tell me why this code appends the field title to the url call when using the pager?

function booking_custom_form_views_exposed_form_alter(&$form, &$form_state, $form_id) {
	
if ($form_id == 'views_exposed_form' && $form_state['view']->name == 'booking_jobs') {

   $form['field_artist_replied_target_id'] = array(
      '#type' => 'checkbox',
      '#title' => t('field_artist_replied_target_id'),
	  '#default_value' => NULL,
	  '#return_value' => $_SESSION['artist_title_nid'],
    );		
  }	
}