I'm sure some of this has been said already, but I haven't read the whole thread.
Can you name a scenario where a part command will actually fail? I can't think of one unless there's some kind of badly written IRCD playing a part.
Since a part command will always succeed, surely it's beneficial to have the window close instantly, rather than wait until the part receipt is received? I can't see any possible reason why somebody would rather have the window close a second after they hit the button (in the case of high lag, could be even longer), rather than instantly.
