Permalink /%postname%/?myown=value is not working

I am running WP multisites, I tried to change the Permalink to /%postname%/ everything is working fine but i am not able to pass any $_GET or $_POST variable to any page, even the contact form 7 stopped.

more info :
– mod_rewrite is enabled.
– .htaccess :
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]
RewriteRule . index.php [L]

</IfModule>

any idea ?