Nginx Rewrites

[grindaland]

Trying to make vBulletin 5.0.0 work with Nginx. Easier said than done!
After a bit of researching and improvising this is what I come up with:

    location /vb5/ {
        rewrite ^/vb5/(.*) /vb5/index.php?routestring=$1 last;
    }

    location /vb5/admincp/ {
        rewrite ^ /vb5/index.php?routestring=admincp/ last;
    }

    location ~ /vb5/(?!index)[^/]+\.php$ {
        rewrite ^/vb5/(.*) /vb5/index.php?routestring=$1 last;
    }

    location ~* ^.+.(jpg|jpeg|css|png|js|ico|xml)$ {
        root /srv/http;
    }

At first glance it SEEMS to work... that is, until you decide to click to one or two links.

This is what happens when I try to login (and then try again (and again (and again (funny, right?)))):



When I instead want to read the FAQs, it nicely notifies me that:

That action could not be completed. Please try again, and if this occurs again please contact the system administrator and tell them how you got this message.

I can't really explore all the function that may or may not work, since I still haven't managed to log into the forums.

Would you please help me figure out how to make these rewrites work (well, assuming the problem isn't elsewhere)?