PUBLIC MARKS with tags clone & ubuntu

with Intel 945GM, Ubuntu 8.04 Hardy, the external VGA monitor is always cloned. Going into System->Preference->Screen Resolution lets you alter the resolution of the LCD and the external monitor, but it stays cloned whether “Clone Screens” is checked or not. Putting monitor to the left or right of the LCD does nothing (stays cloned). However, putting monitor above or below LCD does work (two desktops, one on top of the other).