Index: wp-admin/widgets.php
===================================================================
--- wp-admin/widgets.php	(revision 15542)
+++ wp-admin/widgets.php	(working copy)
@@ -66,7 +66,7 @@
 function retrieve_widgets() {
 	global $wp_registered_widget_updates, $wp_registered_sidebars, $sidebars_widgets, $wp_registered_widgets;
 
-	$_sidebars_widgets = array();
+	$_sidebars_widgets = array( 'wp_inactive_widgets' => array() );
 	$sidebars = array_keys($wp_registered_sidebars);
 
 	unset( $sidebars_widgets['array_version'] );
@@ -90,7 +90,7 @@
 	if ( !empty($sidebars_widgets) ) {
 		foreach ( $sidebars_widgets as $lost => $val ) {
 			if ( is_array($val) )
-				$_sidebars_widgets['wp_inactive_widgets'] = array_merge( (array) $_sidebars_widgets['wp_inactive_widgets'], $val );
+				$_sidebars_widgets['wp_inactive_widgets'] = array_merge( $_sidebars_widgets['wp_inactive_widgets'], $val );
 		}
 	}