Index: Doctrine/Data/Export.php
===================================================================
--- Doctrine/Data/Export.php	(revision 7606)
+++ Doctrine/Data/Export.php	(working copy)
@@ -153,6 +153,7 @@

         foreach ($data AS $className => $classData) {
             $preparedData[$className] = array();
+            $keyType = $classData->getTable()->getIdentifierType();
             foreach ($classData as $record) {
                 $className = get_class($record);
                 $recordKey = $className . '_' . implode('_', $record->identifier());
@@ -168,7 +169,7 @@
                       $keys = array($keys);
                     }

-                    if (count($keys) <= 1 && in_array($key, $keys)) {
+                    if ($keyType!=Doctrine_Core::IDENTIFIER_NATURAL && count($keys) <= 1 && in_array($key, $keys)) {
                         continue;
                     }