SUMMARY

If I configure a new shortcut in Okular for enabling the color modification, when I press this shortcut once, it does work, but after the shortcut is disabled.

STEPS TO REPRODUCE
0. First, in Configuration/Okular configuration/Accessibility/Color modification set some colors rendering options, like "Modify dark and light colors" and choose some colors for the dark and light colors.
1. Go to Configuration > configure keyboard shortcuts
2. Search for the color modification entry (in french "Active/Désactive la modification des couleurs")
3. Set the shortcut to Ctrl+I for example, and press Ok
4. Press Ctrl+I: the color is toggled


OBSERVED RESULT

5. Press Ctrl+I again: nothing happens, the shortcut does not work anymore
6. Check again what is the shortcut for color modification entry: it is reset.

EXPECTED RESULT

I'd expect the shortcut to stay the same after enabling it.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Debian unstable
(available in About System)
KDE Plasma Version: 5.17.5
KDE Frameworks Version: 5.62.0
Qt Version: 5.12.5