Ticket #20601: 20601.diff

wp-includes/query.php

@@ -2304 +2304 @@
                         }
                         $q['author_name'] = sanitize_title_for_query( $q['author_name'] );
                         $q['author'] = get_user_by('slug', $q['author_name']);
-                        if ( $q['author'] )
+                        if ( $q['author'] && is_user_member_of_blog( $q['author']->ID ) )
                                 $q['author'] = $q['author']->ID;
+                        else 
+                                $q['author'] = false;
                         $whichauthor .= " AND ($wpdb->posts.post_author = " . absint($q['author']) . ')';
                 }