SUMMARY If I change the size of the window buttons in the window theme, the change will be applied to all themes, not just to the theme that I'm editing. STEPS TO REPRODUCE 1. Download custom window themes from the KDE store. 2. Go to System Settings -> Application Style -> Window Decorations. 3. Click the edit button for some theme other than the one that's active, and change the icon size. OBSERVED RESULT Nothing should happen in themes other than the one being edited. EXPECTED RESULT Other themes also change their icon size, including the one being currently used, despite not having been edited. SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: (available in About System) KDE Plasma Version: 5.20.5 KDE Frameworks Version: 5.78.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION
I cannot reproduce this on current master. Which themes did you edit? Does this happen for all themes or just a particular one?
Did some testing and it's not between all themes, but it does affect breeze-breeze10: https://github.com/sp1ritCS/Breeze10
There is no global button size, every theme has it's own config. Since Breeze10 is a fork from Breeze it writes to the same settings file, which means when you change Breeze10 you change Breeze too and vice versa. Can you check what happens to e.g. Oxygen when you change Breeze10. It should not be affected.
Oxygen is not affected, and neither is Plastik. I unfortunately uninstalled all other themes so cannot tell exactly which ones are affected.
Then I would suggest to ask the author of Breeze10 to change the config location so it does not interfere with the breeze config. I don't see how kwin does anything wrong here.