[ubuntu] Ubuntu 12.04.1 + Bumblebee 3.0.1 => Flickering screen

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http://ubuntuforums.org – Hello, forum users! I have a laptop Samsung 300v5a-s19 with NVIDIA GeForce GT 520MX. I have just installed Ubuntu 12.04.1 and then Bumblebee 3.0.1. Now it works well without any lags, but there is one problem: when I try to change the screen brightness (by Fn buttons or in the System Settings (Brightness and lock)), display starts flickering. That is, I can not dim the screen. Does anyone know what the problem is and how to solve it? Thanks for your aid. (Hardware)