Problem with $form_state['rebuild']

Here, this is what my form looks like:

function payment_arbitrary_form($form, &$form_state){
  $form_state['payment'] = new Payment(array(
      'context' => 'payment_arbitrary',
      'currency_code' => 'AUD',//todo: Make a setting
      'description' => 'Donation',//Default - will be overwritten
      'finish_callback' => 'payment_arbitrary_payment_finish',
    ));
  
  $form['payment_method'] = array(
    '#access' => TRUE,
    '#type' => 'payment_method',
    '#title' => t('Payment method'),
    '#required' => TRUE,
    '#pmids' => array(),//Todo: Access Checking for payment methods
  );
  $form['payment_amount'] = array(
    '#type' => 'textfield',
    '#title' => t('Payment Amount'),
    '#required' => TRUE,
    );
  $form['payment_description'] = array(
    '#type' => 'textarea',
    '#title' => t('Payment Description'),
    );
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Pay'),
  );
  return $form;
}

So the form displays as expected, I can choose a payment method, fill in the details, and then, when I click the Pay button, nothing happens. payment_arbitrary_form_submit() is never called...

Sure. Very simple module attached. Ignore all the commented code. Enable it and then go to 'payment/new'.

Thanks for your time.

Well, I gave up using '#type' => 'payment_method' and just got the options myself using the following method.

  $payment_methods = entity_load('payment_method', FALSE);
  foreach ($payment_methods as $payment_method) {
    $pmid_options[(string) $payment_method->pmid] = check_plain($payment_method->title_generic);
  }

The arbitrary module is now working. You can see it here: http://drupal.org/sandbox/ChrisGillis/2000394