Index: taxonomy_defaults.module
===================================================================
--- taxonomy_defaults.module	(revision 253)
+++ taxonomy_defaults.module	(working copy)
@@ -93,7 +93,8 @@
 
         if ($visible) {
           // Do not preselect terms on nodes that already have been edited
-          if (!isset($node->nid)) {
+          // or when taxonomy is supposed to be synchronize by i18nsync.module
+          if (!isset($node->nid) && (!$form['#node']->translation_source->taxonomy && in_array('taxonomy', (array)$i18nsync_fields))) {
             $form['taxonomy']['tags'][$vid]['#default_value'] = $typed_string;
           }
         }
@@ -109,7 +110,8 @@
       else {
         if ($visible) {
           // Do not preselect terms on nodes that already have been edited
-          if (!isset($node->nid)) {
+          // or when taxonomy is supposed to be synchronize by i18nsync.module
+          if (!isset($node->nid) && (!$form['#node']->translation_source->taxonomy && in_array('taxonomy', (array)$i18nsync_fields)) ) {
             $form['taxonomy'][$vid]['#default_value'] = $default_tids;
           }
         }