I have a slight issue that makes my desktop wallpaper appear slightly different on desktop #1 compared to the rest. The image is pretty much at a 3:2 resolution so of course it has borders on it. However I notice after a while of being logged in that my wallpaper will stretch to fit the whole screen on desktop #1 and not on desktop 2, 3 and 4 (Not sure if it matters that I have the desktop cube effect enabled) all have the picture at normal aspect. I don't recall ever having this problem before and I've been using Kubuntu for about a year now.
I finally figured out the real way to make sure I don't get the wallpaper stretching anymore. I realized after a while that it was opening Nautilus that caused my desktop icons and wallpaper to stretch, because by default Nautilus handles your desktop and also defaults your desktop back to gnome... Yeah I'm really not a fan of Gnome at all. At any rate type
gsettings set org.gnome.desktop.background show-desktop-icons false
To make gnome applications never change your desktop. This is what has actually worked for me in the long term and I never had to change anything after that to make it work. Also if you have custom icons you should type
sudo apt full-upgrade
to make all parts of your system recognize your new icons.
I want to follow up to this as I semi-solved the problem. I can't pinpoint anything in my terminal stack that indicates when and why this wallpaper stretching error occurs but I have (sort of) a fix for this.
Open terminal and type:
killall plasmashell plasmashell
This only seems to work temporarily, and the wallpaper will still end up stretching after an unknown time interval. Wondering what the hell is going on here. I tried going into the KDE Plasma compositor settings and changing the OpenGL version back and forth from 3.1 to 2.0 and then back again and that does nothing... Something that usually works to fix most graphical errors I get in Plasma. p.s. my KDE Plasma version is 5.8.5