[O] Wrapping section within LaTeX environment

[Xavier Garrido]

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