Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 17602)
+++ wp-includes/query.php	(working copy)
@@ -1510,7 +1510,7 @@
 			$this->parse_tax_query( $qv );
 
 			foreach ( $this->tax_query->queries as $tax_query ) {
-				if ( 'IN' == $tax_query['operator'] ) {
+				if ( ( 'NOT' != $tax_query['operator'] ) && ( 'NOT IN' != $tax_query['operator'] ) ) {
 					switch ( $tax_query['taxonomy'] ) {
 						case 'category':
 							$this->is_category = true;