I did a test with removing the redirection line in .htaccess and nothing has changed, except that http://www.paris-balloon.com/index.html
goes to 404 error page.
This redirection applies only for index.html link:
RedirectPermanent /index.html http://www.paris-balloon.com/index.php
I need this redirection working as many SEO external links still goes to index.html.
I think that one solution is in getting rid of index.php in the home Path but I don't see how to do it. Do you want me to send you a copy of my .htaccess file ?