=== modified file 'includes/common.inc'
--- includes/common.inc	2009-11-08 12:43:40 +0000
+++ includes/common.inc	2009-11-08 21:28:26 +0000
@@ -4936,14 +4936,21 @@ function drupal_render_page($page) {
  */
 function drupal_render(&$elements) {
   static $defaults;
+  // This variable contains the elements to be rendered. Each piece on the stack
+  // is an assocative array with two keys: elements is the parent elements and
+  // key is the actual key. Each POP from the stack is the equivalent of a
+  // drupal_render($elements[$key]) call.
+  $stack = array();
+  $output = '';
+  do {
   // Early-return nothing if user does not have access.
   if (!isset($elements) || (isset($elements['#access']) && !$elements['#access'])) {
-    return;
+      continue;
   }
 
   // Do not print elements twice.
   if (isset($elements['#printed']) && $elements['#printed']) {
-    return;
+      continue;
   }
 
   // Try to fetch the element's markup from cache and return.
@@ -4980,7 +4987,8 @@ function drupal_render(&$elements) {
     }
   }
 
-  // Get the children of the element, sorted by weight.
+    // Get the children of the element sorted by weight. The elements
+    // themselves are sorted, too.
   $children = element_children($elements, TRUE);
 
   // Initialize this element's #children, unless a #pre_render callback already
@@ -4997,8 +5005,18 @@ function drupal_render(&$elements) {
   // This is the same process as drupal_render_children() but is inlined
   // for speed.
   if ($elements['#children'] == '') {
-    foreach ($children as $key) {
-      $elements['#children'] .= drupal_render($elements[$key]);
+      $current_size = count($stack);
+      $new_size = $current_size + count($children);
+      // We need to reverse the array but there is no point to array_reverse
+      // and then add the keys to the stack, both can be done in one loop.
+      for ($i = $current_size; $i < $new_size; $i++) {
+        $stack[$i] = array('elements' => &$elements, 'key' => $children[$new_size - $i -1]);
+      }
+      if ($children) {
+        // Break references. It's not possible to put this in the for header
+        // because unset is not a function but a language construct.
+        unset($elements);
+        continue;
     }
   }
 
@@ -5037,7 +5055,12 @@ function drupal_render(&$elements) {
   }
 
   $elements['#printed'] = TRUE;
-  return $prefix . $elements['#children'] . $suffix;
+    $output .= $prefix . $elements['#children'] . $suffix;
+    // Break references. It's not possible to put this in the for header.
+    unset($elements);
+  // POP a piece from the stack and if succeeded, also load $elements.
+  } while (($data = array_pop($stack)) && ($elements =  &$data['elements'][$data['key']]));
+  return $output;
 }
 
 /**