weird redirect when using .htaccess pointing to a ps in a subfolder

[palermuke]

I have prestashop  1561 in a subfolder. So I used the other users solution to avoid to show /subfolder/ in the URL : ( http://www.prestashop.com/forums/topic/18393-solved-move-prestashop-from-subfolder-to-root/) 

Somehow  redirections  with "www." doesn´t work right for me as for other users. I rechecked the .htaccess file and seems to be all right.

 

 I get this redirections:

 

http://mydomain.com               works: redirects to                      root/subfolder/index.php

http://mydomain.com/en           works

 

http://www.mydomain.com/               shows 404page:                      http://mydomain.com/index.php?

http://www.mydomain.com/en             shows 404page:                      http://mydomain.com/index.php?controller=404
 

Everthing looks correct.  Any Idea about what should I check?
 

friendly URL actived
I changed URI field to "/"
.htaccess :

# Copy and paste the following code into the .htaccess file
# in the public_html folder of your hosting account
# make the changes to the file according to the instructions.
# Do not change this line - RewriteEngine on
RewriteEngine on
# Change yourdomain.com to be your main domain.
RewriteCond %{HTTP_HOST} ^(www.)?mysite.com$
# Change 'subfolder' to be the folder you will use for your main domain.
RewriteCond %{REQUEST_URI} !^/prestashop/
# Don't change this line.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Change 'subfolder' to be the folder you will use for your main domain.
RewriteRule ^(.*)$ /prestashop/$1
# Change yourdomain.com to be your main domain again.
# Change 'subfolder' to be the folder you will use for your main domain
# followed by / then the main file for your site, index.php, index.html, etc.
RewriteCond %{HTTP_HOST} ^(www.)?mysite.com$
RewriteRule ^(/)?$ prestashop/index.php [L]