Ever since I installed Ubuntu 16.04 (fresh, but kept my home directory), I've had a broken wallpaper that I cannot change (i.e. changing the wallpaper doesn't do anything). I tried resetting Unity (unit-tweak-tool --reset-unity) and resetting Compiz (dconf reset -f /org/compiz/). Now I have no wallpaper (black). Still, changing the wallpaper doesn't have any effect.
I also tried creating a new user. The new user works fine and I can change the wallpaper too. In fact, that is why I figured having kept my home directory might be the problem and reset Unity and Compiz.