--- updates.js.orig	2015-04-09 23:16:33.144288113 +0100
+++ updates.js	2015-04-13 23:47:44.238220067 +0100
@@ -538,10 +538,14 @@
 	 * If an update is on-going and a user attempts to leave the page,
 	 * open an "Are you sure?" alert.
 	 */
-	$( window ).on( 'beforeunload', function() {
+	wp.updates.beforeunload = function() {
 		if ( wp.updates.updateLock ) {
 			return wp.updates.l10n.beforeunload;
 		}
-	});
+	}
+
+	$( window ).on( 'beforeunload', function() { wp.updates.beforeunload(); } );
+
+	$( document ).trigger( 'wp-plugin-shinyupdates-loaded' );

 })( jQuery, window.wp, window.pagenow, window.ajaxurl );