--- ckeditor.utils.js (saved version)
+++ (current document)
@@ -89,6 +89,7 @@
     }
   }
 
+  if (Drupal.ckeditorInstance) { Drupal.ckeditorInstance.destroy(true); }
   Drupal.ckeditorInstance = CKEDITOR.replace(textarea_id, textarea_settings);
 };