Wrapping section within LaTeX environment

[Xavier Garrido <xavier.garrido@gmail.com>]

Dear orgers,

I would like to wrap a given org section between =\begin,\end= LaTeX 
environment. These sections are identified by a special tag :correction: 
and to initiate the =\begin= flag I have basically no problem by using 
the  org-export-filter-headline-function filter. The problem comes when 
I want to close the environment i.e. when another section starts. I have 
try this piece of code

#+BEGIN_SRC emacs-lisp
   (setq correction-flag nil)
   (defun cpp-correction-headline (contents backend info)
     (if (and (org-export-derived-backend-p backend 'latex)
                (string-match "\\`.*correction.*\n" (downcase contents)))
         (progn
           (setq correction-flag t)
           (replace-match "\\\\begin{correction}" nil nil contents)
           )
       (when correction-flag
         (setq correction-flag nil)
         (concat "\\end{correction}" contents))
       )
     )
   (add-to-list 'org-export-filter-headline-functions 
'cpp-correction-headline)
#+END_SRC

but I get several =\end{correction}= in the produced LaTeX file. 
Actually this is much more a emacs-lisp related question since the 
boolean =correction-flag= seems not to work and I don't know why (of 
course I have very little knowledge in lisp). Can some emacs-lisp 
experts helps me understand why the above code just does not work.

Thanks a lot,
Xavier