"add field" link on entity display management

Here is some code, but need to be reviewed as it not works properly.
EDIT: missing redirection after field save

ds/modules/ds_extras/ds_extras.admin.inc ~ line 457

  /**
    Add "add field" links
  */
  $form['additional_settings']['add_custom_fields'] = array(
    '#type' => 'fieldset',
    '#group' => 'tabs',
    '#title' => t('Add custom fields'),
    '#weight' => 10,
  );

  $cfields = array();
  $ajaxconf = array(
    'callback' => 'ds_add_field_loadform',
    'wrapper' => 'ds-add-field-target',
    'method' => 'html',
    'effect' => 'fade',
  );

  $cfields['custom_field'] = array(
    '#type' => 'button',
    '#value' => t('Add a field'),
    '#name' => 'custom_field',
    '#weight' => 10,
    '#ajax' => $ajaxconf,
  );    
  // manage_ctools    
  $cfields['manage_ctools'] = array(
    '#type' => 'button',
    '#name' => 'manage_ctools',
    '#value' => t('Add a dynamic field'),
    '#weight' => 20,
    '#ajax' => $ajaxconf,
  );

  if (module_exists('block')) {
    $cfields['manage_block'] = array(
      '#type' => 'button',
      '#name' => 'manage_block',
      '#value' => t('Add a block field'),
      '#weight' => 30,
      '#ajax' => $ajaxconf,
    );
  }    

  $form['additional_settings']['add_custom_fields'] += $cfields;

  $form['additional_settings']['add_custom_fields']['content'] = array(
    '#markup' => "<div class='clear' id='ds-add-field-target'></div>",
    '#weight' => 50,
  );

  /** !eof Add "add field" links
  */

and the callback for ajax

/**
  * ds_add_field_saveform
  * ajax callback after field save callback
  *
  */

function ds_add_field_submit($form, $form_state)
{
//   $commands = array();
//   $commands[] = ajax_command_replace(NULL, "");
//   $commands[] = ajax_command_prepend(NULL, theme('status_messages'));
//   return array('#type' => 'ajax', '#commands' => $commands);

    $form_state['redirect'] = $form_state['storage']['ref'];
//     die("OK ".$form_state['storage']['ref']);
//     drupal_goto($form_state['storage']['ref']);

}

/**
  * ds_add_field_loadform
  * ajax callback to render add field form
  *
  */
// ds_add_field_loadform(null, null);
function ds_add_field_loadform($form, $form_state)
{

  // var_dump($form_state);die();

  switch($_POST['_triggering_element_name'])
  {
  case "manage_ctools":
    $form_name = "ds_edit_ctools_field_form";  
  break;
  case "manage_block":
    $form_name = "ds_edit_block_field_form";
  break;
  default:
    $form_name = "ds_edit_custom_field_form";  
  break;
  }

  module_load_include('inc','ds','ds.fields');
  module_load_include('inc','ds','ds.registry');

  $form = drupal_get_form($form_name);
  
  $menu_cb = _ds_menu();
  foreach($menu_cb as $path=>$mitem)
  {
    if(is_array($mitem['page arguments']) && $form_name == $mitem['page arguments'][0])
    {
      break;
    }
  }
  
  $form['#action'] = url($path);
  $form['#submit'] = array('ds_add_field_submit');
  
  $url = parse_url($_SERVER['HTTP_REFERER']);
//   $form_state['redirect'] = url(substr($url['path'],1));
  $form_state['storage']['ref'] = url(substr($url['path'],1));

  return drupal_render($form);
}

Hi, I've moved the code to a ctools modal avoiding some strangeness in the form building.
I've got two points of doubt in the code, in line 175 and 200 in the patch attached.

* I use $_POST instead $form_state, I can't find how to get it
* Field UI regeneration creates a form_id--N which break the js functionality; still a form_build problem I think

Patch is built upon the latest 7.x-1.x dev branch.

Thanks in advance.

Thanks!
Just in case, I've added a raw refresh $.get-ing the same document.location and reattaching behaviors.