%2F problem in query string

[Davide D'Amico]

Hi, I've this location stanza:
   location ~ \.(gif|jpg|png)$ {
     rewrite ^/images/s/(.*).jpg$ /img.php?f=s&e=$1 break;
     rewrite ^/images/t/(.*).jpg$ /img.php?f=t&e=$1 break;
     proxy_pass http://127.0.0.1:80;
     proxy_cache BACKEND;
     proxy_cache_valid 200 1w;
   }

But if nginx encounters this URL:
62.101.64.91 - app.testsite.com - [01/Oct/2010:12:08:56 +0200]
"GET /images/s/0Atma%2F%2FHrs%2FI%3D.jpg HTTP/1.1" 200 0
"http://app.testsite.com/en/website/parts-express-com?page=1"
"Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.8) Gecko/20100723
Ubuntu/9.04 (jaunty) Firefox/3.6.8" "-" [127.0.0.1:80]

it's rewriting to:

APACHE
62.101.64.91 - - [01/Oct/2010:12:08:58 +0200] "GET
/img.php?f=t&e=0Atma/Hrs/I= HTTP/1.0" 200"

Is it a right behaviour or it's a bug?

Thanks,
d.