Getting weird issue with Nginx reverse Proxy

[blason]

Here is Apache config

<VirtualHost fs.example.com:80>
    ServerAdmin webmaster at example.com
    DocumentRoot /var/www/fs/
        ServerName fs.example.com
        ServerAlias     fs.example.com
        ErrorLog /var/log/apache2/fs/error.log
        CustomLog /var/log/apache2/fs/access.log combined
LogFormat "%{X-Forwarded-For}i %l %u %t \"%r\" %>s %b \"%{Referer}i\"
\"%{User-Agent}i\"" proxy
#SetEnvIf X-Forwarded-For "^.*\..*\..*\..*" forwarded
#CustomLog "logs/access_log" combined env=!forwarded
#CustomLog "logs/access_log" proxy env=forwarded

    <Directory "/var/www/fs/">
        Options Indexes FollowSymLinks Includes ExecCGI
    </Directory>
</VirtualHost>

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,293780,293788#msg-293788