Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 17159)
+++ wp-includes/query.php	(working copy)
@@ -1559,7 +1559,8 @@
 		// Correct is_* for page_on_front and page_for_posts
 		if ( $this->is_home && 'page' == get_option('show_on_front') && get_option('page_on_front') ) {
 			$_query = wp_parse_args($query);
-			if ( empty($_query) || !array_diff( array_keys($_query), array('preview', 'page', 'paged', 'cpage') ) ) {
+			$excluded_vars = array_diff( array_keys($_query), array('preview', 'page', 'paged', 'cpage') );
+			if ( empty($_query) || !empty($excluded_vars) ) {
 				$this->is_page = true;
 				$this->is_home = false;
 				$qv['page_id'] = get_option('page_on_front');