Dynamic select form with onChange attribute, pass an argument to a pre-built view...

I have 2 problems with the following form :

1) default value in the select box is always 1;

2) The pre-built view "league_standings" doesn't show up, when form is submitted automatically through onChange trigger. Still, the function "standings_display" is called.

Edit : I see now that if I add drupal_set_message($view_content); ( see the added code below in comments ), it shows my view as expected !!! of course, it's themed like a normal drupal_set_message and it shows up above my select box, so I don't consider it a solution. So the question becomes : why I can't display anything inside "standings_display" function ? very strange...

Any idea ?

   #hook_menu

   $items['node/%/league_standings']= array(
   'title' => t('Standings'),
   'page callback' => 'drupal_get_form',
   'page arguments' => array('standings_form'),
   'access callback' => 'league_check',
   'access arguments' => array(1),
   'type' => MENU_LOCAL_TASK,
   );

   #hook_form

   function standings_form($form_state) {

   if (!isset($form_state['dropdown'])) {
    $group_nid = 1;
   }
   else {
    $group_nid = $form_state['dropdown'];
   }

   $form['groupset']['dropdown'] = array(
    '#type' => 'select',
    '#title' => t('Group'),
    '#options' => array(
      '1' => t('group 1'),
      '2' => t('group 2'),
      '3' => t('group 3'),
    ),
    '#default_value' => $group_nid,
    '#prefix' => '<div class="clear-block">',
    '#suffix' => '</div>',
    '#attributes' => array('onchange' => "form.submit('dropdown')"),
    '#weight' => 1,
   );

   $form['groupset']['group_nid'] = array(
    '#type' => 'hidden',
    '#value' => $group_nid,
   );

   $form['groupset']['submit'] = array(
    '#type' => 'submit',
    '#value' => 'Display',
    '#submit' => array('standings_display'),
    '#attributes' => array('style' => 'display: none;'),
    '#weight' => 2,
   );

   return $form;

   }

   #submit_function

   function standings_display($form, &$form_state) {
   
   $group_nid = $form_state['values']['group_nid'];
   $viewName = 'league_standings';
   $view_content = views_embed_view($viewName, 'default', $group_nid);
   //drupal_set_message($view_content);
   return $view_content;

   }