ATI HD5570 (VisionTek, fglrx), 4 monitors (3+1), Xinerama

[GTBecker]

I am trying to have a single-monitor desktop able to run maximized video while another three-monitor desktop is in use - but any activity on the three-monitor desktop causes the single-monitor desktop maximized window to restore to its previous un-maximized size and position.

It seems to me that there is no apparent difference between two configurations: four monitors in a single 4x1 desktop (1 RightOf 0, 2 RightOf 1, etc), and three monitors in one desktop plus a single-monitor desktop with Xinerama. Try as a I might, both configurations appear to produce the same result (and no menu on the single desktop). I can drag a window anywhere in either configuration.

Can anyone point at a solution?

Thanks.