Index: hierarchical_select.module
===================================================================
--- hierarchical_select.module	(revision 899)
+++ hierarchical_select.module	(working copy)
@@ -294,6 +294,9 @@ function hierarchical_select_json() {
   // Collect all necessary variables.
   $cached = cache_get($hs_form_build_id, 'cache');
   $storage = $cached->data;
+  if (!$storage) {
+    $storage = unserialize(urldecode($_POST['hierarchical_select_js']));
+  }
 
   // Ensure that the form id in the POST array is the same as the one of the
   // stored parameters of the original form. For 99% of the forms, this step
@@ -734,6 +737,12 @@ function hierarchical_select_after_build
     // render part of the form).
     $hs_form_build_id = 'hs_form_'. md5(mt_rand());
     cache_set($hs_form_build_id, $storage, 'cache', time() + $expire);
+    $form_element = array(
+      '#type' => 'hidden',
+      '#value' => urlencode(serialize($storage)),
+      '#parents' => array('hierarchical_select_js'),
+    );
+    $form['hierarchical_select_js'] = form_builder($form['form_id']['#value'], $form_element, $form_state);
   }
   elseif (isset($_POST['hs_form_build_id'])) {
     // Don't generate a new hs_form_build_id if this is a re-rendering of the