diff -ruN calendar-6.x-2.4-org/calendar.module calendar-6.x-2.4-after-patch/calendar.module
--- calendar-6.x-2.4-org/calendar.module	2010-12-31 16:25:43.000000000 +0000
+++ calendar-6.x-2.4-after-patch/calendar.module	2011-01-18 01:21:43.000000000 +0000
@@ -697,6 +697,7 @@
     // duplicate items from the other date fields, so add a way to
     // make sure each individual date field only gets added to the
     // calendar one time.
+    $base_field_hack = ($view->base_field == 'nid');
     $processed = array();
     $rrule_processed = array();
     foreach ($items as $pos => $item) {
@@ -706,7 +707,8 @@
         $real_field = str_replace(array('_value2', '_value'), '', $field_name);
       }
       
-      $id = 'calendar.'. $item->{$view->base_field} .'.'. $real_field .'.'. $delta;
+      // $id = 'calendar.'. $item->{$view->base_field} .'.'. $real_field .'.'. $delta;
+      $id = 'calendar.'. ($base_field_hack ? $item->raw->nid : '') .'.'. $item->{$view->base_field} .'.'. $real_field .'.'. $delta;
       
       // When creating iCal feeds for repeating dates we don't want all
       // the multiple values, send only the first value.