Way back in the GC2 beta days, they had similar problems with alt-tab crashing the game. Windowed mode worked a lot better, and setting the window resolution equal to the desktop size - to get the effect of full screen but avoid the alt-tab problems - kind of got recommended as the best way to play. I've been away from Stardock betas since then, so I don't know their history, but it might be that for Elemental it's deliberately behaving this way.