I know I've run into a similar issue like this in the past. More importantly, /close should work on all windows including channels. This is more intuitive than using /part to close a channel window. /part implies leaving... if you're not in a channel but the window is open, using /part really makes little sense.
Also... there are times when you want to /part a channel and leave the window open. Or you are on freenode and someone performs a /remove command on you (sending a part event to your client and causing the window to close).
