Ticket #39758: 39758.2.patch

src/wp-includes/nav-menu-template.php

@@ -397 +397 @@
                 // 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 it is the customize page then it will strips the query var off the url before entering the comparison block.
+                        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 ) );