emacs 24, tramp and history causing sudo tramp to fail

[Richard Riley <rileyrg@googlemail.com>]

here's a little bug which I came across and am wondering if I can
configure it out.

Open a file and then re-Open it as root 

I use

(defun find-alternative-file-with-sudo ()
  "Open current buffer as root!"
  (interactive)
  (when buffer-file-name
    (find-alternate-file
     (concat "/sudo:root@localhost:"
	     buffer-file-name))))


edit, save, quit the file.

open some more files.

now C-x C-f and use M-p to find a previous file name in the open
history. The problem is that the tramp sudo line is one of the history elements and
as soon as it comes into the minibuffer input it triggers a background
password process causing all further sudo opens to fail.

regards
r.