Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 17231)
+++ wp-includes/query.php	(working copy)
@@ -1696,7 +1696,8 @@
 			$tax_query[] = array(
 				'taxonomy' => 'category',
 				'terms' => $q['category__in'],
-				'field' => 'term_id'
+				'field' => 'term_id',
+				'include_children' => false
 			);
 		}
 
@@ -1706,6 +1707,7 @@
 				'taxonomy' => 'category',
 				'terms' => $q['category__not_in'],
 				'operator' => 'NOT IN',
+				'include_children' => false
 			);
 		}