ORIG_PATH_INFO breaks default route

[eluser]krif[/eluser]
Okay, this might or might not be a bug. I am stuck with a certain setup that I don't want to change mucht since I seem to be veeeery close to the solution

For a certain reason (specific URL tracking with query strings appended) I want to use ORIG_PATH_INFO as uri_protocol.

Everything works fine for me with one exception: the default route is not working. When I try to access

http://www.myserver.com/ or
http://www.myserver.com/index.php - results in a CI generated 404
http://www.myserver.com/index.php/ - works perfect though. (Note the trailing slash)

I have no idea though why my CI installation throws a 404 instead of calling the default controller. I tried setting the index page to '' or 'index.php' but neither helped.

(I have these rules in my htaccess:

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php/home/index/$1 [QSA,NC,L]

but even when I completely comment them out, the problem persists, so it seems like that has nothing to do with that.)

I'd be happy for any hack or hints that lead me to where CI checks the requested URL and in this case doesn't seem to realize that it should call the default route.

[eluser]krif[/eluser]
Why is it that I always come up with answers right after I posting somewhere but not for the hours before?

I just set a route for 'index.php' and that worked. Still would curious why it didn't work in the first place ...