About write-contents-functions in pre-test 24.0.95.1

[Chming]

Hello,

I am using the following codes to untabify code in c mode.

;; Untabify when saving
(defun ska-untabify ()
  (save-excursion
    (goto-char (point-min))
    (when (search-forward "\t" nil t)
      (untabify (1- (point)) (point-max)))
    nil))

(defun saving-untabify ()
  (add-hook 'write-contents-functions 'ska-untabify nil t))
(add-hook 'c-mode-common-hook 'saving-untabify)

Right now when I try this on the latest version, it looks like it will
remove all tabs in makefile mode. My understanding is this func only
works on cc-mode. Is that correct to use write-contents-functions in
this way?

Thanks a lot.

Ming