button face vs font-lock

[Thien-Thi Nguyen <ttn@gnuvola.org>]

Greetings,

I'm trying to implement a simple toggle button, using:

 (define-button-type 'toggle
   'mouse-face nil
   'follow-link t
   'help-echo nil
   'active nil
   'face 'button
   'action (lambda (button)
             (let ((now (not (button-get button 'active))))
               (button-put button 'active now)
               (button-put button 'face (if now
                                            font-lock-keyword-face
                                          'button))
               (message "%s %s" (button-label button) now))))
 
 (insert-text-button "abc" :type 'toggle)

This works fine when font-lock is off (M-x font-lock-mode RET),
but when i enable font-lock, the button refuses to change face,
although the toggling is still evidenced in the echo area.

What do i need to do get font lock to leave dynamic button
face changing alone?

thi