Index: src/wp-includes/nav-menu-template.php
===================================================================
--- src/wp-includes/nav-menu-template.php	(revision 40375)
+++ src/wp-includes/nav-menu-template.php	(working copy)
@@ -397,6 +397,9 @@
 		// if the menu item corresponds to the currently-requested URL
 		} elseif ( 'custom' == $menu_item->object && isset( $_SERVER['HTTP_HOST'] ) ) {
 			$_root_relative_current = untrailingslashit( $_SERVER['REQUEST_URI'] );
+            if ( is_customize_preview() ) {
+                $_root_relative_current = strtok( untrailingslashit( $_SERVER['REQUEST_URI'] ), '?' );
+            }
 			$current_url = set_url_scheme( 'http://' . $_SERVER['HTTP_HOST'] . $_root_relative_current );
 			$raw_item_url = strpos( $menu_item->url, '#' ) ? substr( $menu_item->url, 0, strpos( $menu_item->url, '#' ) ) : $menu_item->url;
 			$item_url = set_url_scheme( untrailingslashit( $raw_item_url ) );