Index: class-wp-customize-widgets.php
===================================================================
--- class-wp-customize-widgets.php	(revision 28796)
+++ class-wp-customize-widgets.php	(working copy)
@@ -1138,7 +1138,7 @@
 	 * @return string Widget instance's hash key.
 	 */
 	protected function get_instance_hash_key( $instance ) {
-		$hash = md5( AUTH_KEY . serialize( $instance ) );
+		$hash = md5( wp_salt( 'auth' ) . serialize( $instance ) );
 		return $hash;
 	}