[O] org-export-latex-final-hook not working

[Giacomo M]

Dear all,

I am using emacs with this configuration file:
#+BEGIN_SRC emacs-lisp
(setq load-path (append (file-expand-wildcards "~/.emacs.d/elpa/*") load-path))
(require 'org)
(require 'org-ref)
(require 'ox-extra)
(ox-extras-activate '(ignore-headlines))
(defun remove-orgmode-latex-labels ()
  "Remove labels generated by org-mode"
  (interactive)
  (let ((case-fold-search nil))
   (goto-char 1)
   (replace-regexp "\\\\label{sec.*}" "")
   )
)
(add-hook 'org-export-latex-final-hook 'remove-orgmode-latex-labels)
#+END_SRC

to load the latest orgmode from melpa and install a hook to remove 
unwanted section labels on latex export.

If you open/create any .org file and export it to latex buffer or file, 
the hook function is not called. if I visit the buffer and call 
remove-orgmode-latex-labels, section labels are removed.

Where is the mistake?

Thanks,

Giacomo

GNU Emacs 24.5.1 (x86_64-w64-mingw32)
Org-mode version 8.3.4 (8.3.4-47-gaf853d-elpa)