I guess that the button is indeed there to make it possible to use alt+space. It's probably not meant to be clicked. That's why it is invisible. Personally, I

I guess that the button is indeed there to make it possible to use alt+space. It's probably not meant to be clicked. That's why it is invisible. Personally, I still use alt-space when somebody has managed to move a window out of the screen: you can still activate it, but you cannot see it. At least practical for me, who never uses Windows, but gets called when people are stuck.