Sun Type 7 Keyboard + KDE shortcuts: Why does the control center ignore most of the function keys on the left edge

I've recently equipped my OpenSuSE 15.2 with KDE 5 with a Sun Type 7 keyboard and now would like to use the function keys on its left edge for a variety of system-wide shortcuts. The only issue is that in the shortcut list of KDE's control center, some of these keys are simply ignored:

The Help, Cut, Copy, Paste, and Open keys are recognised as such, whereas Cancel, Redo, Undo, Properties, Foreground, and Find are not, and I don't know why. All of them emit their own scancodes, and xkb maps them to the corresponding key symbols. Here is, for instance, what the Properties key emits (output from xev):

KeyPress event, serial 40, synthetic NO, window 0x7800001,
    root 0x561, subw 0x0, time 3103717, (-256,541), root:(1374,570),
    state 0x10, keycode 138 (keysym 0x1005ff70, SunProps), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

What's wrong with these keys? Here is my xkb config for your reference:

╭─jacek@epica ~  
╰─➤  setxkbmap -verbose 10
Setting verbose level to 10
locale is C
Trying to load rules file ./rules/evdev...
Trying to load rules file /usr/share/X11/xkb/rules/evdev...
Success.
Applied rules from evdev:
rules:      evdev
model:      pc102
layout:     de
variant:    pl
options:    terminate:ctrl_alt_bksp,altwin:meta_win,lv3:ralt_switch,compose:menu
Trying to build keymap using the following components:
keycodes:   evdev+aliases(qwertz)
types:      complete
compat:     complete
symbols:    pc+de(pl)+inet(evdev)+terminate(ctrl_alt_bksp)+altwin(meta_win)+level3(ralt_switch)+compose(menu)+terminate(ctrl_alt_bksp)
geometry:   pc(pc102)

UPDATE: I've looked into the current xkb config to find out that in the symbols/inet file, there is a complete block devoted to the proprietary Sun Type 6/7 function keys:

partial alphanumeric_keys
xkb_symbols "evdev" {
    key <MUTE>   {      [ XF86AudioMute         ]       };
    key <VOL->   {      [ XF86AudioLowerVolume  ]       };
    key <VOL+>   {      [ XF86AudioRaiseVolume  ]       };
    key <POWR>   {      [ XF86PowerOff          ]       };
    key <STOP>   {      [ Cancel                ]       }; // KDE ignores me!
    key <AGAI>   {      [ Redo                  ]       }; // KDE ignores me!
    key <PROP>   {      [ SunProps              ]       }; // KDE ignores me!
    key <UNDO>   {      [ Undo                  ]       }; // KDE ignores me!
    key <FRNT>   {      [ SunFront              ]       }; // KDE ignores me!
    key <COPY>   {      [ XF86Copy              ]       };
    key <OPEN>   {      [ XF86Open              ]       };
    key <PAST>   {      [ XF86Paste             ]       };
    key <FIND>   {      [ Find                  ]       };
    key <CUT>    {      [ XF86Cut               ]       };
    key <HELP>   {      [ Help                  ]       };
    key <LNFD>   {      [ Linefeed              ]       };
};

This means that the keycodes and symbols are registered in xkb the right way, but unfortunately, it's KDE's control center, which ignores the Sun-specific keysyms (see the comments above). Does that mean that I'll have to file a ticket with the KDE guys?