How to reproduce:
1) Set the Breeze sddm theme background image (1.jpg) with the sddm kcm.
2) Try to change the Breeze sddm theme background image with the same name (1.jpg) with the sddm kcm.
As the 'clear image' action is not removing the image file from the "/usr/share/sddm/themes/breeze/" the user needs to change the background image to another name (2.jpg) before the old name can be used again.
*** This bug has been marked as a duplicate of bug 381382 ***
sorry, that's not quite the same.
I did get around this by having the image for the SDDM a link instead. Keep in mind that you have to make the link in /usr/share/sddm/themes/breeze/ for this to work properly.
The gist of it: `ln -s 1.jpg /usr/share/sddm/themes/breeze/`
After this you can change 1.jpg in any way you want and SDDM will listen to you.
For more info see here:
Fixed with https://cgit.kde.org/sddm-kcm.git/commit/?id=dc1922e6aa486500cb3d4cfeb0243bb2f5fdeb25
This bug persists in plasma 5.15.2.
I used files named "2.jpg" instead of "1.jpg".
Operating System: Arch Linux
KDE Plasma Version: 5.15.2
KDE Frameworks Version: 5.55.0
Qt Version: 5.12.1
We check the file name every time to save uploading a new wallpaper if we've adjusted something unrelated like the cursors. Should be fixable if we track the dirty state client side.
Once a new SDDM theme is selected and rebooted, the correct theme shows while logging in. Once the laptop sleeps and is awakened it reverts back to the default SDDM theme.
This is still the case with KDE Plasma version 5.27.7.
The old background isn't deleted, therefore it isn't possible to set a new background when it has the same filename.