No need to apologize. Now we have the answer in case the problem comes up again. Thanks for figuring it out.

So sorry. Initially, I too didn't think dexpot would be at fault, but it seemed very repeatable.

After shutting all other programs off, one I realized I couldn't switch off was ATI's Catalyst Control Center (CCC).

Digging in CCC's options it turns out that it has a "Desktop Manager", in tab Hydravision | Desktop Manager (This is different than its MultiDesktop options). Switching the Desktop Manager off in CCC immediately solved the problem. It must be turned on by default during install in multi-monitor applications, as I don't ever recall switching it on. Sorry for the false alarm and the trouble!

Is there nothing else that could be causing this? It's not reproducible on any of our test systems and Dexpot doesn't even use the Windows function to change monitor positions.

Minor bug to report.

On Win 7x64 with Dexpot 1.6.4 Build 2186, I have two monitors, physically side-by-side with desktop extended horizontally across both.

If i change a virtual desktop's background in Dexpot (Configure Desktops | background tab), it changes the orientation of the monitors from side-by-side to top-to-bottom. This also changes how Dexpot spans an image (if that mode is set). I can manually change the orientation back in the usual Windows desktop settings or ATI Catalyst Control Center, after which, Dexpot also will correctly span the image.

Can post pictures if that's helpful, or problem isn't clear by description.