FTP idle connections get reset before timeout

I have a Windows 2003 Standard Server. When I connect via FTP, if I remain
idle for a minute and a half to 2 minutes, my connection gets disconnected
(though my server thinks I am still connected). My timeout is set to 300
seconds and increasing it even further has no effect. This happens on both
active and passive modes, with multiple clients, and from multiple places.

If I completely disable Windows Firewall, the problem goes away. I have been
told that this is a known issue with ALG and there is no way to fix it short
of not using the built-in Firewall.

Has anyone else had this problem and been able to fix it?