Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 13682)
+++ wp-includes/query.php	(working copy)
@@ -1875,7 +1875,7 @@
 			$q['cat'] = $reqcat;
 
 			$join = " INNER JOIN $wpdb->term_relationships ON ($wpdb->posts.ID = $wpdb->term_relationships.object_id) INNER JOIN $wpdb->term_taxonomy ON ($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id) ";
-			$whichcat = " AND $wpdb->term_taxonomy.taxonomy = 'category' ";
+			$whichcat .= " AND $wpdb->term_taxonomy.taxonomy = 'category' ";
 			$in_cats = array($q['cat']);
 			$in_cats = array_merge($in_cats, get_term_children($q['cat'], 'category'));
 			$in_cats = "'" . implode("', '", $in_cats) . "'";
@@ -1961,7 +1961,7 @@
 			if ( count($post_ids) )
 				$whichcat .= " AND $wpdb->posts.ID IN (" . implode(', ', $post_ids) . ") ";
 			else {
-				$whichcat = " AND 0 = 1";
+				$whichcat .= " AND 0 = 1";
 				break;
 			}
 		}