Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 21662)
+++ wp-includes/taxonomy.php	(working copy)
@@ -658,8 +658,9 @@
 		$join = '';
 		$where = array();
 		$i = 0;
+		$count = count( $this->queries );
 
-		foreach ( $this->queries as $query ) {
+		foreach ( $this->queries as $index => $query ) {
 			$this->clean_query( $query );
 
 			if ( is_wp_error( $query ) ) {
@@ -671,9 +672,11 @@
 			if ( 'IN' == $operator ) {
 
 				if ( empty( $terms ) ) {
-					if ( 'OR' == $this->relation )
+					if ( 'OR' == $this->relation ) {
+						if ( $index + 1 === $count && empty( $where ) )
+							return self::$no_results;
 						continue;
-					else
+					} else
 						return self::$no_results;
 				}