Monkey patch for #31484: Widgets appearing in Customizer preview during a theme preview may not correspond to controls in Widgets panel

trac-31484-monkey-patch.js

/*global wp */

(function ( api ) {
	/**
	 * Mark a sidebars_widgets setting as dirty.
	 *
	 * @param {wp.customize.Setting} setting
	 */
	var markAddedSidebarsWidgetsAsDirty = function ( setting ) {
		if ( 0 === setting.id.indexOf( 'sidebars_widgets[' ) ) {
			setting._dirty = true;
		}
	};

	// Only mark settings initially added as dirty
	api.bind( 'add', markAddedSidebarsWidgetsAsDirty );
	api.bind( 'ready', function () {
		api.unbind( 'add', markAddedSidebarsWidgetsAsDirty );
	});
}( wp.customize ));

trac-31484-monkey-patch.php

<?php
/**
 * Plugin Name: Trac #31484 Monkey Patch
 * Description: Fix: Widgets appearing in Customizer preview during a theme preview may not correspond to controls in Widgets panel.
 * Plugin URI: https://gist.github.com/westonruter/c0b94561ec1adac966af
 * Version: 0.1
 * Author: XWP, Weston Ruter
 * Author URI: https://xwp.co/
 * License: GPLv2+
 */

/**
 * Copyright (c) 2015 XWP (https://xwp.co/)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License, version 2 or, at
 * your discretion, any later version, as published by the Free
 * Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */

function trac_31484_monkey_patch_enqueue_scripts() {
	/**
	 * @var WP_Customize_Manager $wp_customize
	 */
	global $wp_customize;

	// The fix is only needed when previewing a different theme
	if ( $wp_customize->is_theme_active() ) {
		return;
	}

	$handle = 'trac-31484-monkey-patch';
	$src = plugin_dir_url( __FILE__ ) . 'trac-31484-monkey-patch.js';
	$deps = array( 'customize-controls' );
	wp_enqueue_script( $handle, $src, $deps );
}
add_action( 'customize_controls_enqueue_scripts', 'trac_31484_monkey_patch_enqueue_scripts' );