Possible bug with the custom wallpaper selection
I go to the Desktop Settings, and choose a different location where my custom wallpapers are (say in my Home/Photos). I then select a wallpaper. All good. My Lightdm is setup to pick up the wallpaper image for the login background. However it will not. The background will be black and no image shown. Even after a restart.
In other words, Lightdm cannot pick up the desktop wallpaper.