My dual screen wallpapers don't line up correctly

I'm running dual 1080p monitors, one is lower than the other so I configured that in the settings. When i tile my wallpaper across both screens, the bottom of the wallpaper lines up with the higher monitor, so the top of the image ends up tiled in the bottom to fill the gap. Here's a screenshot to show what i mean:

Note the stars on the bottom of the left screen.

Now I had it working fine before i reimaged last week. So i'm on a fresh install of windows with a brand new "feature". Does anyone know how to fix this?