Disco Dingo 19.04 background error
I have an temporarily fix for this problem, Luckly it's very very easy.
press: alt + f2 ,to open a command screen
type: r
press: enter
that's all, the backgrounds have reloaded. its not a fix but it helps till this problem is patched
source: https://www.fosslinux.com/3495/how-to-refresh-desktop-in-ubuntu-without-rebooting-pc.htm
btw some laptops requite to press alt + fn + f2