Description of problem:

Plasma uses subpixel RGB font rendering by default. You can disable it in plasma font settings by selecting "None" option in subpixel rendering section.
However, while doing that correctly disables subpixel rendering, option itself is stuck and if you go to font settings after that it will show "RGB"

Version-Release number of selected component (if applicable):

Fedora 32, 33
Plasma versions 5.18, 5.19, 5.20 (through copr)

Steps to Reproduce:

1. Open font settings in kde control center
2. Change subpixel rendering option from RGB to None and click Apply
3. Close control center and repeat step 1

Actual results: subpixel font rendering section will show "RGB" value

Expected results: subpixel font rendering section should show previously selected None value

Additional info:

This looks like this bug, reported to KDE bugzilla: https://bugs.kde.org/show_bug.cgi?id=416140
However i have reasons to believe this is Fedora specific, because:
1) Font rendering options is actually applied correctly in my case
2) I can not reproduce the same behaviour on other distributions with KDE  (OpenSUSE, Manjaro, Kubuntu) for specified versions
Could it be some fedora specific static configuration file (in etc?) that makes kcm go haywire?