Wrong cache front page with any GET parameters.

I have multicurrency field type, which generates a field value and prefix based on GET parameter and COOKIE. COOKIE is the first condition, GET parameter - the second one.

And use hook_url_outbound_alter() to rewrite all links with adding of the query_string values needed.

So, i have following path types: site.com/?c=EUR | site.com/?c=USD | site.com

Without boost cache -it works.

With enabled boost cache i get the same content of front page with any types of GET['c'].

On other pages the boost works as well.