Double Session ID in my URL, why?

Hello Community,

i add the session-id to my url, but sometimes, php will automatically
add the same session id.

my problem is like this: index.php?MySID=123456789&MySID=123456789

why add php the session id automatically to the url? can i deactivte
this?

i try the following, but without any results:
ini_set("session.use_cookies", "on");
ini_set("session.use_trans_sid", "off");

can anybody help my?

sry for my bad englisch, i hope you understand me.

greetz and thanks for help me.