Injecting rendered form with an Ajax command.

I need to change the form displayed on a page using ajax.

I created an ajax command (having class CommandInterface). The command is called from JavaScript on the client, which in turns sets a callback command that takes the rendered form markup and injects it in a <div>. The form is displayed, but when submit is clicked, the page redirects to: http://as.local/outline/form_action_p_pvdeGsVG5zNF_XLGPTvYSKCf43t8qZYSwc.... The url is a hardcoded value that acts as a placeholder (hardcoded in the Drupal core FormBuilder class).

This issue exists on the D8 Outline module development version (code below is from that module), available at https://www.drupal.org/project/outline. If you download and install this module, and create a simple outline, and set the outline's "render as" setting to "Form", you can reproduce the issue.

Here is the client js code that calls the command:

     ...
      var url = 'outline/render-entry/' +
          type + '/' +
          id + '/' +
          render + '/' +
          mode;
      var ajax = Drupal.ajax({
        url: Drupal.url(url)
      });
      ajax.execute();

Here is the render method of the Ajax Command class:

  /**
   * {@inheritdoc}
   */
  public function render() {

    // Get the entity.
    $entity = \Drupal::entityTypeManager()
      ->getStorage($this->type)
      ->load($this->id);

    // Create render array.
    if ($this->render == Entry::RENDER_AS_DISPLAY) {
      $renderArray =
        \Drupal::entityTypeManager()
          ->getViewBuilder($this->type)
          ->view($entity, $this->mode);
    }
    elseif ($this->render == Entry::RENDER_AS_FORM) {
      $form = \Drupal::service('entity.manager')
        ->getFormObject('outline_entry', 'default')
        ->setEntity($entity);
      $renderArray = \Drupal::formBuilder()->getForm($form);
    }

    // Return the markup.
    $markup = \Drupal::service('renderer')->render($renderArray);
    return [
      'command' => 'renderEntry',
      'renderedEntry' => $markup,
    ];
  }

Here is the "renderEntry" command that is called on the client:

  Drupal.AjaxCommands.prototype.renderEntry = function (ajax, response, status) {
    var renderedEntry = response.renderedEntry;
    var entryContainer = $('.entry-container');
    entryContainer.html(renderedEntry);
    var form = entryContainer.find('form')[0];
    Drupal.attachBehaviors(form, Drupal.settings);
  };