Index: field_group.module
===================================================================
--- field_group.module	(revision 234)
+++ field_group.module	(working copy)
@@ -1518,7 +1518,7 @@
 function field_group_unpack($group) {
 
   // Extract unserialized data.
-  if (isset($group->data)) {
+  if (!empty($group->data)) {
     $data = $group->data;
     unset($group->data);
     $group->label = $data['label'];