I have built svn server on my nginx webserver. my nginx configuration is

server {
        listen  80;
        server_name svn.mysite.com;
        location / {
        access_log off;
        proxy_pass http://svn.mysite.com:81;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }
        location ~ \.php$ {
                fastcgi_pass 127.0.0.1:9000;
                fastcgi_index index.php;
                include fastcgi_params;
        }
}

Now, i can svn co and svn up normally without having any problem and when i try to commit i get error:

$svn up
At revision 1285.
$ svn info
Path: .
URL: http://svn.mysite.com/elpis-repo/crons
Repository Root: http://svn.mysite.com/elpis-repo
Repository UUID: 5303c0ba-bda0-4e3c-91d8-7dab350363a1
Revision: 1285
Node Kind: directory
Schedule: normal
Last Changed Author: alaa
Last Changed Rev: 1280
Last Changed Date: 2012-04-29 10:18:34 +0300 (Sun, 29 Apr 2012)

$svn st
M       config.php
$svn ci -m "Just a test, add blank line to config" config.php
Sending        config.php
svn: Commit failed (details follow):
svn: File 'config.php' is out of date
svn: '/elpis-repo/!svn/bc/1285/crons/config.php' path not found

if i try to svn co on port 81 (my proxy_pass which is apache) and then svn ci, it will work smoothly! but why it doesn't work when i use nginx to accomplish it?
any idea is highly appreciated.