Index: wp-admin/includes/post.php
===================================================================
--- wp-admin/includes/post.php	(revision 16485)
+++ wp-admin/includes/post.php	(working copy)
@@ -1146,12 +1146,12 @@
 		return false;
 
 	$lock = get_post_meta( $post->ID, '_edit_lock', true );
-	$last = get_post_meta( $post->ID, '_edit_last', true );
+	list( $user, $time ) = explode( ':', $lock );
 
 	$time_window = apply_filters( 'wp_check_post_lock_window', AUTOSAVE_INTERVAL * 2 );
 
-	if ( $lock && $lock > time() - $time_window && $last != get_current_user_id() )
-		return $last;
+	if ( $time && $time > time() - $time_window && $user != get_current_user_id() )
+		return $user;
 	return false;
 }
 
@@ -1166,12 +1166,13 @@
 function wp_set_post_lock( $post_id ) {
 	if ( !$post = get_post( $post_id ) )
 		return false;
-	if ( 0 == get_current_user_id() )
+	if ( 0 == ($user_id = get_current_user_id()) )
 		return false;
 
 	$now = time();
+	$lock = "$user_id:$now";
 
-	update_post_meta( $post->ID, '_edit_lock', $now );
+	update_post_meta( $post->ID, '_edit_lock', $lock );
 }
 
 /**
@@ -1182,7 +1183,8 @@
  */
 function _admin_notice_post_locked() {
 	global $post;
-	$last_user = get_userdata( get_post_meta( $post->ID, '_edit_last', true ) );
+	list( $user, $time ) = explode( ':', get_post_meta( $post->ID, '_edit_lock', true ) );
+	$last_user = get_userdata( $user );
 	$last_user_name = $last_user ? $last_user->display_name : __('Somebody');
 
 	switch ($post->post_type) {