Yes, I've seen that many times. And it happens with PS3 players too, as they need a bit for it to load. That's why, most of the time when I see anyone doing that, I step back and enjoy the views from behind the wall, specially when they've been asked to wait a bit. If they're in such a rush that they can't wait 30s max., they can eat the extra seconds/minutes that will take them to kill the bosses without another one. I for one don't mind alt tabbing meanwhile