diff -u b/core/lib/Drupal/Component/Utility/Html.php b/core/lib/Drupal/Component/Utility/Html.php
--- b/core/lib/Drupal/Component/Utility/Html.php
+++ b/core/lib/Drupal/Component/Utility/Html.php
@@ -22,24 +22,11 @@
   protected static $classes = array();
 
   /**
-   * An array of the initial IDs used in one request.
-   *
-   * @var array
-   */
-  protected static $seenIdsInit;
-
-  /**
-   * An array of IDs, including incremented versions when an ID is duplicated.
-   * @var array
-   */
-  protected static $seenIds;
-
-  /**
-   * Contains the current AJAX HTML IDs.
+   * A random string added to ids to ensure uniqueness.
    *
    * @var string
    */
-  protected static $ajaxHTMLIDs;
+  protected static $request_nonce;
 
   /**
    * Prepares a string for use as a valid class name.
@@ -130,16 +117,14 @@
    *   The cleaned ID.
    */
   public static function getUniqueId($id) {
-    $request_nonce = &drupal_static(__FUNCTION__ . ':nonce');
-    if (!isset($request_nonce)) {
+    if (!isset(static::$request_nonce)) {
       // @todo The hash should not change for sub-requests, so it is not clear
       //   whether relying on the Request object is appropriate. Verify this,
       //   once there are sub-requests in core.
-      $request_nonce = uniqid();
+      static::$request_nonce = uniqid();
     }
 
-    $id .= '-' . $request_nonce;
-    return Html::getId($id);
+    return Html::getId($id) . '-' . static::$request_nonce;
   }
 
   /**