I'm global keys CTRL+F1 can't redefine to NULL values in control panel. This option return old value CTRL+F1. I'm use KDENeon distributive.
I'am set in programm System Parameters: -> Combination keys -> Global combination keys -> Plasma -> Make widget "Classic application menu" -> Default (not defined) This parameters not saved and equally old value "Other CTRL+F1"
This was fixed in Plasma 5.20.