=== modified file 'sites/all/modules/nat/nat.admin.inc'
--- sites/all/modules/nat/nat.admin.inc	2010-07-15 11:50:29 +0000
+++ sites/all/modules/nat/nat.admin.inc	2010-07-14 14:44:31 +0000
@@ -58,9 +58,17 @@
     $form['nat_'. $type]['node_links_'. $type] = array(
       '#type' => 'checkbox',
       '#title' => t('Make NAT terms in %type node views point to the associated node rather than the taxonomy page.', array('%type' => $type)),
+      '#description' => t('Note that this is option is <em>not</em> usually turned on for the node type which has a vocabulary enabled for NAT (in this settings screen), but for other node types which allow users to select terms from a NAT-enabled vocabulary.'),
       '#default_value' => isset($nat_config['node_links'][$type]) ? $nat_config['node_links'][$type] : 0,
       '#parents' => array('node_links', $type)
     );
+    $form['nat_'. $type]['reuse_terms_'. $type] = array(
+      '#type' => 'checkbox',
+      '#title' => t('Reuse existing terms.'),
+      '#default_value' => isset($nat_config['reuse_terms'][$type]) ? $nat_config['reuse_terms'][$type] : 0,
+      '#description' => t('By default, new terms will always be created in the selected vocabularies, upon creating a new node (and during Sync). Checking this option will instead create an association to an <em>existing</em> term with the same name, if possible. (If multiple terms with the same name exist in a vocabulary, an association is made to one of the terms. Matching is case insensitive.)'),
+      '#parents' => array('reuse_terms', $type)
+    );
   }
   $form['submit'] = array('#type' => 'submit', '#value' => t('Save configuration'));
 
@@ -77,8 +85,9 @@
 
   $form_values['body'] = array_filter($form_values['body']);
   $form_values['delete'] = array_filter($form_values['delete']);
+  $form_values['related'] = array_filter($form_values['related']);
   $form_values['node_links'] = array_filter($form_values['node_links']);
-  $form_values['related'] = array_filter($form_values['related']);
+  $form_values['reuse_terms'] = array_filter($form_values['reuse_terms']);
 
   variable_set('nat_config', $form_values);
 

=== modified file 'sites/all/modules/nat/nat.module'
--- sites/all/modules/nat/nat.module	2010-07-15 11:50:29 +0000
+++ sites/all/modules/nat/nat.module	2010-07-14 14:44:58 +0000
@@ -480,11 +480,14 @@
  */
 function _nat_add_terms($node, $vids = array()) {
   $nat_config = _nat_variable_get();
+  $existing_terms = array();
+  if (isset($nat_config['reuse_terms'][$node->type])) {
+    $existing_terms = taxonomy_get_term_by_name($node->title);
+  }
 
   $edit = array(
     'name' => $node->title,
     'description' => isset($nat_config['body'][$node->type]) ? $node->body : '',
-    'weight' => 0
   );
 
   $tids = array();
@@ -497,13 +500,17 @@
     unset($edit['tid']);
 
     $edit['vid'] = $vid;
+    $edit['weight'] = 0;
+    foreach ($existing_terms as $eterm) {
+      if ($eterm->vid == $vid) {
+        // Update the existing term, just as in _nat_update_terms()
+        $edit['tid'] = $eterm->tid;
+        $edit['weight'] = $eterm->weight;
+      }
+    }
+
     // Save hierarchy for vocabularies also present in the node form.
-    if (isset($hierarchy[$vid])) {
-      $edit['parent'] = $hierarchy[$vid];
-    }
-    else {
-      $edit['parent'] = array();
-    }
+    $edit['parent'] = isset($hierarchy[$vid]) ? $hierarchy[$vid] : array();
     $edit['relations'] = isset($node->nat) && isset($node->nat['related'][$vid]) ? $node->nat['related'][$vid] : array();
     $edit['synonyms'] = isset($node->nat) ? $node->nat['synonyms'] : '';
 
@@ -598,7 +605,8 @@
       'body' => array(),
       'delete' => array(),
       'related' => array(),
-      'node_links' => array()
+      'node_links' => array(),
+      'reuse_terms' => array(),
     );
     $variables = variable_get('nat_config', array());
     $variables = array_merge($defaults, $variables);