URL Rewriting & $_POST data

Question

I have see many answers to this topic, but none ssem to work for me, or I don't understand the answers (...), so, if anyone has the patience to re-explain / review my particular and apparently simple issue, I'd be really grateful:

I have the following rewrite rules in my .htacces:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
# RewriteRule ^ index.php [L]

RewriteRule ^pour-tous-les-ages index.php?p=shop.ages
RewriteRule ^tous-les-fabricants index.php?p=shop.fabricants
RewriteRule ^toutes-les-rubriques index.php?p=shop.rubriques
RewriteRule ^choix-des-creches index.php?p=shop.creches
RewriteRule ^toutes-les-nouveautes index.php?p=shop.new
RewriteRule ^les-promotions index.php?p=shop.discounted
RewriteRule ^listes-de-naissance index.php?p=wishlists
RewriteRule ^liste-de-naissance index.php?p=wish.show

They all "work" as expected, except for the last one :

RewriteRule ^liste-de-naissance index.php?p=wish.show

This particular url ('index.php?p=wish.show') should have $_POST DATA 'attached' to it. As for many people out there, the $_POST data is not preserved, and I can't figure out why... the form in index.php?p=wishlists the has a select for choosing the 'wishlist's ID, carried over via POST request to the "index.php?p=wish.show" URL this URL correctly goes to the proper MVC method, but, the POST data is...lost... What might be missing, what are my doing wrong ? Many thanks for your help BR, JM