--- taxonomy_defaults.module.orig	2012-05-16 15:39:42.183734001 +0100
+++ taxonomy_defaults.module	2012-05-16 15:43:27.311733669 +0100
@@ -67,6 +67,7 @@
 function taxonomy_defaults_form_alter(&$form, &$form_state, $form_id) {
   // Only alter node forms
   if (isset($form['type']) && $form['type']['#value'] .'_node_form' == $form_id) {
+    $is_preview = isset($form_state['node_preview']);
     $node = $form['#node'];
 
     // Retreive the core forum vocabulary id so it can be skipped later
@@ -91,13 +92,13 @@
         }
         $typed_string = taxonomy_implode_tags($terms, $vid);
 
-        if ($visible) {
+        if ($visible && !$is_preview) {
           // Do not preselect terms on nodes that already have been edited
           if (!isset($node->nid)) {
             $form['taxonomy']['tags'][$vid]['#default_value'] = $typed_string;
           }
         }
-        else {
+        else if (!$visible) {
           // For hidden vocabs, we just assign the defaults without checking for existing terms.
           // It's a bit brutal to assume this is OK, but so is the alternative, and this keeps the forms clean.
           $form['taxonomy']['tags'][$vid] = array(
@@ -107,13 +108,13 @@
         }
       }
       else {
-        if ($visible) {
+        if ($visible && !$is_preview) {
           // Do not preselect terms on nodes that already have been edited
           if (!isset($node->nid)) {
             $form['taxonomy'][$vid]['#default_value'] = $default_tids;
           }
         }
-        else {
+        else if (!$visible) {
           // For hidden vocabs, we just assign the defaults without checking for existing terms.
           // It's a bit brutal to assume this is OK, but so is the alternative, and this keeps the forms clean.
           $form['taxonomy'][$vid] = array(