I managed to get a "quick look" window into a different space. So. It's not visible on the screen with mailmate. If I try to close the window, I am moved back to the mailmate space. As soon as I go back to the space with that window, it's visible again.
I was able to move it by dragging it off the side of the screen until it reached the right space, but that was a pretty cool failure state. -s
