The macro with-current-notmuch-show-message executes command
`notmuch show --format=raw id:...` which just outputs the contents
of the mail file verbatim (into temporary buffer). In case e.g. utf-8
locale is used the temporary buffer has buffer-file-coding-system as
utf-8. In this case Emacs converts the data to multibyte format, guessing
that input is in utf-8.
However, the "raw" (MIME) message may contain octet data in any other
8bit format, and as no (MIME-)content spesific handling to the message
is done at this point, conversion to other formats may lose information.
By setting coding-system-for-read 'no-conversion drops the conversion part
and makes this handle input as notmuch-get-bodypart-internal() does.
This marks the broken test in previous change fixed.
---
 emacs/notmuch-show.el | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 5b3e70e..44b6f35 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -203,9 +203,10 @@ For example, if you wanted to remove an \"unread\" tag and add a
      (let ((id (notmuch-show-get-message-id)))
        (let ((buf (generate-new-buffer (concat "*notmuch-msg-" id "*"))))
          (with-current-buffer buf
-	    (call-process notmuch-command nil t nil "show" "--format=raw" id)
-           ,@body)
-	 (kill-buffer buf)))))
+	   (let ((coding-system-for-read 'no-conversion))
+	     (call-process notmuch-command nil t nil "show" "--format=raw" id)
+	     ,@body)
+	   (kill-buffer buf))))))
 
 (defun notmuch-show-turn-on-visual-line-mode ()
   "Enable Visual Line mode."
-- 
1.8.0