Index: wp-includes/widgets.php
===================================================================
--- wp-includes/widgets.php	(revision 11673)
+++ wp-includes/widgets.php	(working copy)
@@ -964,10 +964,12 @@
 	if ( is_admin() ) {
 		$sidebars_widgets = get_option('sidebars_widgets', array());
 	} else {
-		if ( empty($_wp_sidebars_widgets) )
+		if ( empty($_wp_sidebars_widgets) ) {
 			$sidebars_widgets = get_option('sidebars_widgets', array());
-		else
+		} else {
 			$sidebars_widgets = &$_wp_sidebars_widgets;
+			$sidebars_widgets['array_version'] = 3;
+		}
 	}
 	$_sidebars_widgets = array();