Kharon - probably not the cause for you but exact same happened to me, I have a touch-screen desktop, flies were the cause of the problem, they land on the screen and manage to change the setting! Touch-screen now switched off!
(When other weird and uncommanded things have happened to the visual it was caused by one of the 'side' buttons on the mouse sticking).
Last edited by parabellum; 9th Oct 2014 at 06:09.