I believe I have identified a problem area for ioFTPD though I have no idea why 6.x is more prone to crashing than 5.x in the situation described below, but it is.
Applications such as netlimiter and nvidia's firewall load a dll into each application's address space so they can catch/manage internet connections. If you will remember I had a terrible time figuring out what was going on during shutdown with all sorts of crashing until I figured out netlimiter might be at fault and uninstalled it. That cleared up all my problems locally.
Based on some crash information from a user and the closesocket deaths from before I knew where to look and sure enough it looks like nvidia's firewall is at fault. FYI: It appears that utorrent also thinks nvidia's firewall is crap because they warn you about it if they notice it's installed. That's how bad it is, they actually look for it in the installer! So, uh, avoid it
Anyway, the good news is I think I solved that person's very frequent crashing, but it doesn't help the rest of us... Ah well.
Programs to avoid:
Netlimiter (1.3, and later?) try BWMeter instead perhaps.
NVidia's firewall