File: calendar/theme/theme.inc
--- theme.inc	2009-02-27 15:10:35.000000000 +0100
+++ theme.inc	2009-03-15 17:48:17.000000000 +0100
@@ -243,6 +243,7 @@
   $view = drupal_clone($vars['view']);
   $rows = $vars['rows'];
   $months = array();
+  $old_month = $view->date_info->month;
   foreach ($rows as $month => $month_rows) {
     $view->date_info->month = $month;
     $view->date_info->granularity = 'month';
@@ -259,6 +260,7 @@
   $vars['months'] = $months;
   $vars['view']->date_info->hide_nav = FALSE;
   $vars['view']->date_info->granularity = 'year';
+  $vars['view']->date_info->month = $old_month;
   
 }