Index: wp-includes/post.php
===================================================================
--- wp-includes/post.php	(revision 12498)
+++ wp-includes/post.php	(working copy)
@@ -1621,10 +1621,6 @@
 		$post_category = array(get_option('default_category'));
 	}
 
-	//Set the default tag list
-	if ( !isset($tags_input) )
-		$tags_input = array();
-
 	if ( empty($post_author) )
 		$post_author = $user_ID;
 
@@ -1767,9 +1763,9 @@
 		$wpdb->update( $wpdb->posts, array( 'post_name' => $data['post_name'] ), $where );
 	}
 
-	wp_set_post_categories( $post_ID, $post_category );
+	wp_set_post_categories( $post_ID, $post_category );
 	// old-style tags_input
-	if ( !empty($tags_input) )
+	if ( isset($tags_input) )
 		wp_set_post_tags( $post_ID, $tags_input );
 	// new-style support for all tag-like taxonomies
 	if ( !empty($tax_input) ) {