Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 16600)
+++ wp-includes/query.php	(working copy)
@@ -701,6 +701,14 @@
 	var $query;
 
 	/**
+	 * Most recent query in serialized form
+	 *
+	 * @access private
+	 * @var string
+	 */
+	var $last_query;
+
+	/**
 	 * Query vars, after parsing
 	 *
 	 * @since 1.5.0
@@ -1247,6 +1255,11 @@
 	 * @param string|array $query
 	 */
 	function parse_query($query) {
+		if ( $this->last_query == serialize($query) ) {
+			return;
+		}
+		$this->last_query = serialize($query);
+
 		if ( !empty($query) || !isset($this->query) ) {
 			$this->init();
 			$this->query = $this->query_vars = wp_parse_args($query);