Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 13459)
+++ wp-includes/taxonomy.php	(working copy)
@@ -19,19 +19,18 @@
 												 	'update_count_callback' => '_update_post_term_count',
 													'label' => __('Categories'),
 													'singular_label' => __('Category'),
-													'query_var' => false,
+													'query_var' => 'category_name',
 													'rewrite' => false,
 													'public' => true,
 													'show_ui' => true,
 													'_builtin' => true
 												) ) ;
 
-	register_taxonomy( 'post_tag', 'post', array(
-												 	'hierarchical' => false,
+	register_taxonomy( 'post_tag', 'post', array(	'hierarchical' => false,
 													'update_count_callback' => '_update_post_term_count',
 													'label' => __('Post Tags'),
 													'singular_label' => __('Post Tag'),
-													'query_var' => false,
+													'query_var' => 'tag',
 													'rewrite' => false,
 													'public' => true,
 													'show_ui' => true,