Comment 8 for bug 993432

Could be related, yes. I also have two monitors, and when going full-screen it sometimes jumps to the wrong monitor. But when losing and then regaining focus it often jumps to a different workspace - or appears to. Showing Expo mode shows it in the different workspace, and when I go there to move it back to the right one, it sometimes jump right back, so I'm not sure if it ever really left the correct workspace. I think so, but it's hard to prove without debugging it.