Index: src/wp-includes/js/customize-base.js
===================================================================
--- src/wp-includes/js/customize-base.js	(revision 26232)
+++ src/wp-includes/js/customize-base.js	(working copy)
@@ -176,8 +176,9 @@
 			to = this.validate( to );
 
 			// Bail if the sanitized value is null or unchanged.
-			if ( null === to || this._value === to )
+			if ( null === to || _.isEqual( from, to ) ) {
 				return this;
+			}
 
 			this._value = to;
 
Index: src/wp-includes/script-loader.php
===================================================================
--- src/wp-includes/script-loader.php	(revision 26232)
+++ src/wp-includes/script-loader.php	(working copy)
@@ -360,7 +360,7 @@
 
 	$scripts->add( 'hoverIntent', "/wp-includes/js/hoverIntent$suffix.js", array('jquery'), 'r7', 1 );
 
-	$scripts->add( 'customize-base',     "/wp-includes/js/customize-base$suffix.js",     array( 'jquery', 'json2' ), false, 1 );
+	$scripts->add( 'customize-base',     "/wp-includes/js/customize-base$suffix.js",     array( 'jquery', 'json2', 'underscore' ), false, 1 );
 	$scripts->add( 'customize-loader',   "/wp-includes/js/customize-loader$suffix.js",   array( 'customize-base' ), false, 1 );
 	$scripts->add( 'customize-preview',  "/wp-includes/js/customize-preview$suffix.js",  array( 'customize-base' ), false, 1 );
 	$scripts->add( 'customize-controls', "/wp-admin/js/customize-controls$suffix.js", array( 'customize-base' ), false, 1 );