[gnome] compiz opacity not happening automatically

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http://ubuntuforums.org – Clean install - Ubuntu 12.04, Gnome classic Compiz's opacity effect (move mouse away from window, it becomes transparent so that I can see the window(s) below) works. But it does not start automatically, despite ticking the box in the opacity section to make it do so. Every session I have to open the compiz settings manager, go do opacity, untick start automatically, and then re-tick. Only THEN will opacity start working. Does anyone know why? Thanks. (Hardware)