I created a wallpaper using DualWallpaper and it all works just great, but when I try to change to another theme, the wallpaper doesn't change to the theme wallpaper. The DualWallpaper I created continues to display no matter which theme I pick. I tried deleting the DualWallpaper.bmp file but nothing changes.
Which version of Windows are you using?
I've just tried it with 7 and I find that changing the theme will override the wallpaper set by DualWallpaper as expected.