EOG does not open focused

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http://unix.stackexchange.com – Something wrong started few days ago. I'm using Ubuntu 10.04 with Gnome. When I double click on a image file, the Eye of Gnome (EOG) opens and shows the image. But the problem is that the focus remains on the Nautilus' window so that if I press Alt+F4 the image remains opened but Nautilus is closed. (HowTos)