UPDATE:!:!:!:!
right...1981, do you use any kind of launcher program like launcher pro etc? because if so you MAY have turned 'scrolling wallpapers' off.....and when they dont scroll multiwallpaper will only have ONE picture for all screens...be it 2 or 7 screens....
I know cos stupidly I had this happen to me hence my lil confusion above..
once the scrolling wallpapers are back on, multiwallpaper will allow different wallpapers to each screen...and if you then select for EACH screen in the options to select a wallpaper from a folder...then everytime you double tap on EACH screen it will just change THAT screen not all and certainly not all to the same wallpaper..