So it's not philosophy. Either it works or it doesn't.
So after /join global joins. You click on the chat, you can write "move to new window", etc.
But sometimes (unfortunately too often) chat is bugging.
U see chat, u cant text on it, cant click to add text after u click "O" and chat when u click "leave" nothing happen!
I did alt+f4 of game, i entered game. Nothing came from global chat. I typed /join global. NOTHING appeared on my "O" -> "chat" window but i started getting messages from global on chat. When i clicked on it to text, still nothing...
Do you use weakauras? Because that seems to bug it like that for me. You need to disable weakauras, get it how you want it again, then enable it again. I have to do it pretty often as well, don't know another workaround.