Update to Drupal 8.2.2. For more information, see https://www.drupal.org/project/drupal/releases/8.2.2

core/modules/outside_in/src/Ajax/OpenOffCanvasDialogCommand.php

@@ -14,8 +14,10 @@ class OpenOffCanvasDialogCommand extends OpenDialogCommand {
   /**
    * Constructs an OpenOffCanvasDialogCommand object.
    *
-   * Drupal provides a built-in offcanvas tray for this purpose, so no selector
-   * needs to be provided.
+   * The off-canvas dialog differs from the normal modal provided by
+   * OpenDialogCommand in that a off-canvas has built in positioning and
+   * behaviours. Drupal provides a built-in off-canvas tray for this purpose,
+   * so the selector is hard-coded in the call to the parent constructor.
    *
    * @param string $title
    *   The title of the dialog.
@@ -46,15 +48,10 @@ class OpenOffCanvasDialogCommand extends OpenDialogCommand {
    * {@inheritdoc}
    */
   public function render() {
-    return [
-      'command' => 'openDialog',
-      'selector' => '#drupal-offcanvas',
-      'settings' => $this->settings,
-      'data' => $this->getRenderedContent(),
-      'dialogOptions' => $this->dialogOptions,
-      'effect' => 'fade',
-      'speed' => 1000,
-    ];
+    $build = parent::render();
+    $build['effect'] = 'fade';
+    $build['speed'] = 1000;
+    return $build;
   }
 
 }

core/modules/outside_in/src/Tests/Ajax/OffCanvasDialogTest.php

@@ -39,7 +39,7 @@ class OffCanvasDialogTest extends AjaxTestBase {
       'data' => $dialog_contents,
       'dialogOptions' =>
         [
-          'title' => 'AJAX Dialog contents',
+          'title' => 'AJAX Dialog & contents',
           'modal' => FALSE,
           'autoResize' => FALSE,
           'resizable' => 'w',