--- a/wp-includes/script-loader.php
+++ b/wp-includes/script-loader.php
@@ -400,7 +400,7 @@
 	$scripts->add( 'backbone', '/wp-includes/js/backbone.min.js', array( 'underscore', 'jquery' ), '1.5.0', 1 );
-	// Backbone was previously version 1.5.0
+	// Updated Backbone to 1.6.1
+	$scripts->add( 'backbone', '/wp-includes/js/backbone.min.js', array( 'underscore', 'jquery' ), '1.6.1', 1 );

--- a/wp-includes/js/backbone.js
+++ b/wp-includes/js/backbone.js
@@
-// Placeholder for old Backbone.js content
+// Replaced with Backbone.js v1.6.1 code from https://github.com/jashkenas/backbone

--- a/wp-includes/js/backbone.min.js
+++ b/wp-includes/js/backbone.min.js
@@
-// Placeholder for old Backbone.min.js content
+// Replaced with Backbone.min.js v1.6.1 code from https://github.com/jashkenas/backbone