$request_uri for subrequest

Hi,

I have problems setting up SSI with NGinx and PHP5-FPM. The problem I
have
is (indrectly) related to this rule

fastcgi_param REQUEST_URI $request_uri;

During the SSI-subrequest the variable $request_uri still points to the
URI
used for the initial request. Asking me, this behavior is questionable
anyway. However, now I have issues finding the real request uri for
the
subrequest, because when I use $uri instead, the request itself works,
but
this also uses the already rewritten.

I’ve started with the common pattern for a Symfony2 project [1]. When I
set

fastcgi_param REQUEST_URI $uri$is_args$args

Nginx passes the full path name /app.php/foo/bar for every request,
even
if it’s not wanted.

Is there’s a reliable way to determine the original subrequest uri? Is
it
possible, that the behaviour of $request_uri for SSI can be treated as
bug?

Thanks for your attention,
Regards,
Sebastian

[1]