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.
The window activates when it is created, but mIRC will not activate it again when the LIST completes. Instead mIRC makes a "ding" sound when the list is completed, and the channels list is highlighted with red text in the switchbar/treebar at the same time (if it's not currently the activate window). All this seems like good behavior to me.