org.el (org-fast-tag-selection): Fix an bug when listing tags for completion.

* org.el (org-fast-tag-selection): Fix an bug when listing
tags for completion.

Thanks to Mike McLean for reporting this.

lisp/org.el

@@ -13695,10 +13695,11 @@ Returns the new tags string, or nil to not change the current settings."
 		  (condition-case nil
 		      (setq tg (org-icompleting-read
 				"Tag: "
-				(append (or buffer-tags
-					    (with-current-buffer buf
-					      (org-get-buffer-tags)))
-					(mapcar 'car table))))
+				(delete-dups
+				 (append (or buffer-tags
+					     (with-current-buffer buf
+					       (mapcar 'car (org-get-buffer-tags))))
+					 (mapcar 'car table)))))
 		    (quit (setq tg "")))
 		  (when (string-match "\\S-" tg)
 		    (add-to-list 'buffer-tags (list tg))