Exportable edit form does not obey $form_state['rebuid'] = true; if you add a button with a #submit function

Description:

I have an exportables item edit form and I have added some handling for an "add more" button to allow for multiple values on a specific field. If I visit this form without javascript enabled, the form submits completely and I am redirected to the /admin/structure/myexportable page even though the submit function that is triggered by my "add more" button is correctly run and $form_state['rebuild'] = TRUE; is correctly set.

How to reproduce:

• I've attached a test module called "foo". It creates an exportable called a foo_bar.
• install the foo module
• add a new "foo_bar" (admin/structure/foo_bar/add)
• click the "BTN TEST" button
• Notice by the dsm() that we correctly run foo_bar_test_submit(). And also notice that that function sets $form_state['rebuild'] = TRUE;

Expected behavior

I would expect that the "add/edit" form should be rebuilt and displayed again instead of the admin/structure/foo_bar page. I should only be redirected to that page on a subimt if rebuild===FALSE.

Some relavant code

In case you dont want to download/install the test module.. here is the relavant code from foo_export_ui.inc:

/**
 * @file
 * A Ctools Export UI plugin for DFP ads.
 */

/**
 * Define this Export UI plugin.
 */
$plugin = array(
  'schema' => 'foo_bar',
  'access' => 'access content',

  // Define the menu item.
  'menu' => array(
    'menu item' => 'foo_bar',
    'menu prefix' => 'admin/structure',
    'menu title' => 'Foo Bars',
    'menu description' => 'Create and manage your foo bars.',
  ),

  // Define user interface texts.
  'title singular' => t('Foo bar'),
  'title plural' => t('Foo bars'),
  'title singular proper' => t('Foo bar'),
  'title plural proper' => t('Foo bar'),

  // Define the class to use as a handler for DFP ad tags.
  'handler' => array(
     'class' => 'foo_bar_ui',
     'parent' => 'ctools_export_ui',
  ),

  // Define the names of the functions that provide the add/edit forms.

  'form' => array(
    'settings' => 'foo_bar_form',
    'submit' => 'foo_bar_form_submit',
    'validate' => 'foo_bar_form_validate',
  ),
);

/**
 * Form builder.
 */
function foo_bar_form(&$form, &$form_state) {
  $form['thing'] = array(
    '#type' => 'textfield',
    '#title' => t('Thing'),
    '#required' => TRUE,
    '#maxlength' => 128,
  );
  $form['machinename'] = array(
    '#type' => 'machine_name',
    '#title' => t('Unique Name'),
    '#maxlength' => 128,
    '#machine_name' => array(
      'exists' => 'foo_bar_name_exists',
      'source' => array('thing'),
    ),
  ) + $form['info']['machinename'];
  unset($form['info']);

  $form['btn'] = array(
    '#type' => 'submit',
    '#value' => 'BTN TEST',
    '#submit' => array('foo_bar_btn_test_submit'),
  );
}

function foo_bar_form_submit($form, &$form_state) {
  dpm('in foo_bar_form_submit');
}

function foo_bar_form_validate(&$form, &$form_state) {
  dpm('in foo_bar_form_validate');
}

function foo_bar_btn_test_submit($form, &$form_state) {
  $form_state['rebuild'] = TRUE;
  dpm('in foo_bar_test_submit');
}

/**
 * Check if the given machinename is unique in the dfp_tags table.
 */
function foo_bar_name_exists($machinename) {
  $select = db_select('foo_bar', 'fb');
  $select->addExpression('COUNT(*)');
  $select->condition('fb.machinename', $machinename);

  return $select->execute()->fetchField();
}