=== modified file 'includes/common.inc'
--- includes/common.inc	2009-12-03 02:20:28 +0000
+++ includes/common.inc	2009-12-05 08:41:57 +0000
@@ -5197,7 +5197,7 @@ function drupal_render_cache_get($elemen
  * @param $elements
  *   A renderable array.
  */
-function drupal_render_cache_set($markup, $elements) {
+function drupal_render_cache_set($markup, &$elements) {
   // Create the cache ID for the element.
   if (!in_array($_SERVER['REQUEST_METHOD'], array('GET', 'HEAD')) || !$cid = drupal_render_cid_create($elements)) {
     return FALSE;
@@ -5210,7 +5210,11 @@ function drupal_render_cache_set($markup
   }
   $bin = isset($elements['#cache']['bin']) ? $elements['#cache']['bin'] : 'cache';
   $expire = isset($elements['#cache']['expire']) ? $elements['#cache']['expire'] : CACHE_PERMANENT;
-  cache_set($cid, $data, $bin, $expire);
+  // Allow for ESI tie ins. @see http://drupal.org/node/651902
+  $return = cache_set($cid, $data, $bin, $expire);
+  if (is_string($return)) {
+    $elements['#children'] = $return;
+  }
 }
 
 /**