Windows spanning 2 monitors resize themselves onto 1 after screen saver is started (Win XP)

Windows spanning 2 monitors resize themselves onto 1 after screen saver is started (Win XP)

I have a dual monitor setup with an ATI Radeon HD 3450 driving 2 Dell 1907FPs in Extended mode. The video driver is ATI's 8.561-081201a1-073177C-Dell.