switching away from guake terminal sometimes doesn't work

I'm using guake on Cinnamon in full-screen mode. I also run tmux in the guake terminal. I have Alt-Space configured to switch the terminal on and off. Switching out of the terminal is sometimes flaky. I'm not sure, but it might be that the problem only occurs when I am running Firefox.

Sometimes when I hit Alt-Space from the Guake terminal nothing happens (but it always seems to work after a few tries). When it fails to work, I often notice that the pointer briefly changes shape to what it would be if the switch had worked. Sometimes the pointer starts switching between these two shapes rapidly and doesn't stop until I succeed in switching away from guake. Also, sometimes it starts displaying half the screen as the guake terminal, as if I were not in full screen mode (but when I switch back to the terminal it is full screen again).