I have a triple monitor setup with the middle screen being my primary. When spanning a single image across the 3 screens the wallpaper is aligned wrong making the image look like:  instead of in order: . In the preferences tab the option to drag and drop screens to realign them has no effect on how the wallpaper is spread. Am I understanding the option wrong or is it not working?
Firstly, you need to change wallpaper after changing order, it isn't automatic. But perhaps, the function don't work as you want, I think I need do some change to correct that.