--- feeds_tamper.module.orig	2013-03-10 21:22:52.000000000 +0200
+++ feeds_tamper.module	2013-03-10 21:18:13.015699297 +0200
@@ -50,7 +50,10 @@
     foreach ($blank_mappings as $blank) {
       $item[$blank] = '';
     }
-    foreach ($importer_instances as $element_key => $instances) {
+    foreach ($mappings as $maps_item) {
+      $element_key = drupal_strtolower($maps_item['source']);
+      $instances = $importer_instances[$element_key];
+
       if (isset($item[$element_key])) {
         foreach ($instances as $instance) {
           $plugin = $plugins[$instance->plugin_id];