Synch with Gnus trunk:

;; I've committed this change to only the trunk by mistake, sorry,
;; but it should have been also in the branch.)
(message-generate-headers): Record insertion of optional headers as well.
Otherwise the check to prevent repeated insertion of optional headers
is a no-op.  By Andreas Seltenreich <seltenreich@gmx.de>.

lisp/gnus/ChangeLog

@@ -1,3 +1,9 @@
+2010-04-22  Andreas Seltenreich  <seltenreich@gmx.de>
+
+	* message.el (message-generate-headers): Record insertion of optional
+	headers as well.  Otherwise the check to prevent repeated insertion of
+	optional headers is a no-op.
+
 2010-04-17  Teodor Zlatanov  <tzz@lifelogs.com>
 
 	* smime.el: Don't mention CVS.

lisp/gnus/message.el

@@ -5880,6 +5880,7 @@ Headers already prepared in the buffer are not modified."
 		      (if formatter
 			  (funcall formatter header value)
 			(insert header-string ": " value))
+		      (push header-string message-inserted-headers)
 		      (goto-char (message-fill-field))
 		      ;; We check whether the value was ended by a
 		      ;; newline.  If not, we insert one.