Index: wp-includes/classes.php
===================================================================
--- wp-includes/classes.php	(revision 11893)
+++ wp-includes/classes.php	(working copy)
@@ -266,7 +266,7 @@
 				$this->query_vars[$wpvar] = $_POST[$wpvar];
 			elseif (!empty($_GET[$wpvar]))
 				$this->query_vars[$wpvar] = $_GET[$wpvar];
-			elseif (!empty($perma_query_vars[$wpvar]))
+			elseif (isset($perma_query_vars[$wpvar]))
 				$this->query_vars[$wpvar] = $perma_query_vars[$wpvar];
 
 			if ( !empty( $this->query_vars[$wpvar] ) ) {