problem with active mode. socket error?

Hello.

I have a problem with ioftpd running in active mode, when the user is behind nat.
Im running ioFTPD version: 5-8-5r

Ive told my users who are behind nat to forward some ports, and tell their ftp clients to use those ports for data transfer. and it works..
BUT, it seems that ioftpd isnt closing sockets.

If i forward 2 ports, i can recive data 2 times, then i have to wait for sockets to close, ~1 min.

Ive searched the forum and found a simular thread, about windows socket API being a prob when server is running on lownumber ports, and only lownumber ports.

But my server isnt on a low number port.. its on a port above 2000.
So i dont know if this is the same prob?

Any help getting around this would be VERY appriciated. Can you get ioftpd to close sockets sooner?

Since many of my users are behind NAT, this is a very big problem. :-/

Thnx in advance /jesper