Contextual filters are broken in the Views UI preview

     $args = array();
-    if (!empty($form_state['values']['view_args'])) {
-      $args = explode('/', $form_state['values']['view_args']);
+    if (!empty($form_state['input']['view_args'])) {
+      $args = explode('/', $form_state['input']['view_args']);
     }

This is the only change i'm not sure why it's needed, even $form_state['values'] is filled on the rebuild request,
it doesn't work as expect, so we maybe need investigation.

Finally figured it out.

• You just want to render the view once the submit function got runned
• Therefore set the renderPreview property so the view only gets the $form_state['values']['view_args'] once

+++ b/core/modules/views/lib/Drupal/views/Tests/UI/PreviewTest.phpundefined
@@ -0,0 +1,52 @@
+   * Tests the settings for the edit ui.

we never c&p in tests, we never do :)

+++ b/core/modules/views/lib/Drupal/views/Tests/UI/PreviewTest.phpundefined
@@ -0,0 +1,52 @@
+    $this->drupalLogin($this->adminUser);

No need for that, the UITestBase does this for us.