Index: newsletter.module
===================================================================
--- newsletter.module	(revision 2871)
+++ newsletter.module	(working copy)
@@ -442,7 +442,7 @@
   field_create_field($field);
 
   $instance = array(
-    'field_name' => 'field_' . $vocabulary->machine_name,
+    'field_name' => 'field_' . $field_name,
     'entity_type' => 'newsletter_template',
     'bundle' => 'newsletter_template',
     'label' => $vocabulary->name,