problem with appointments not cancelling

[Richard G Riley <rileyrgdev@googlemail.com>]

I have the following in one of my org files but the reminder is still
popping up (or was until the original scheduled time was passed). What
do I need to call to have a cancelled org entry removed from the
reminder mechanism? I use the gtk reminder system and include the code
below. Does the org-agenda-to-appt not remove closed/cancelled entries?
(Note I changed the run-at-time parameters to run now and repeat every
while).

1) org entry

** CANCELED gf 
   SCHEDULED: <2008-08-26 Tue 14:00> CLOSED: [2008-08-26 Tue 13:50]

2) code

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; For org appointment reminders

; 5 minute warnings
(setq appt-message-warning-time '15)
(setq appt-display-interval '5)

; Update appt each time agenda opened.
(add-hook 'org-finalize-agenda-hook 'org-agenda-to-appt)

; Setup zenify, we tell appt to use window, and replace default function
(setq appt-display-format 'window)
(setq appt-disp-window-function (function my-appt-disp-window))

(defun my-appt-disp-window (min-to-app new-time msg)                      
  (save-window-excursion (shell-command (concat 
    "/usr/bin/zenity --info --title='Appointment' --text='" 
    msg
    "' &"
    ) nil nil)
))

;; activate and schedule refresh
(appt-activate t)
(run-at-time nil 3600 'org-agenda-to-appt)