comint and font-lock in CVS emacs

[Jay Belanger <belanger@truman.edu>]

For some reason, comint and font-lock don't play well in CVS emacs.
If I define a mode that calls comint-mode, and then tries to do some
font-locking, such as

(defun my-mode ()
  "..."
  (interactive)
  (comint-mode)
  (make-local-variable 'font-lock-defaults)
  (setq font-lock-defaults 
        '((my-font-lock-keywords my-font-lock-keywords-1 
           my-font-lock-keywords-2 my-font-lock-keywords-3)
          nil t))
  ...

The font-locking is ignored, although it works well in emacs 21.2.
Has something about comint-mode changed?  (I didn't see anything
relevant in the Changelog.)
(I'm not sure why I didn't use define-derived-mode, but when I change
it to that, the font-locking works, but the fonts on the input line
get overridden but the input face; in 21.2, the input face properties
get added to the font-locking.)

Jay