Index: wp-includes/post.php
===================================================================
--- wp-includes/post.php	(revision 13283)
+++ wp-includes/post.php	(working copy)
@@ -2179,8 +2179,7 @@
 
 	wp_set_post_categories( $post_ID, $post_category );
 	// old-style tags_input
-	if ( !empty($tags_input) )
-		wp_set_post_tags( $post_ID, $tags_input );
+	wp_set_post_tags( $post_ID, $tags_input );
 	// new-style support for all tag-like taxonomies
 	if ( !empty($tax_input) ) {
 		foreach ( $tax_input as $taxonomy => $tags ) {