That's a fair point. mIRC should probably only load up the window when it receives 321.
That's the bug IMO, not that it shows the window on disconnection.
I guess we could also discuss whether mIRC should activate the list window when it "finishes" (I can't confirm, is that what it's doing?). It should probably highlight the switchbar/taskbar, but not activate the window when a list completes. Activating the window [if that's what it does] seems way too obtrusive, even if you're still connected when it happens.