Index: wp-includes/widgets.php
===================================================================
--- wp-includes/widgets.php	(revision 19317)
+++ wp-includes/widgets.php	(working copy)
@@ -1190,8 +1190,12 @@
 
 		unset( $sidebars_widgets['wp_inactive_widgets'] );
 
-		foreach ( $wp_registered_sidebars as $id => $settings )
-			$_sidebars_widgets[$id] = array_shift( $sidebars_widgets );
+		foreach ( $wp_registered_sidebars as $id => $settings ) {
+			if ( isset( $sidebars_widgets[$id] ) ) {
+				$_sidebars_widgets[$id] = $sidebars_widgets[$id];
+				unset( $sidebars_widgets[$id] );
+			}
+		}		
 
 		$orphaned = 0;