Gnome Tweak Tool - Miscellaneous compatibility options - Apple Aluminium Keyboard: emulate PC keys is broken

I'm on Ubuntu 17.04
Gnome Tweak Tool says it is version GNOME Shell v3.24.2 (classic mode)

When I enable "Gnome Tweak Tool/Typing/Miscellaneous compatibility options/Apple Aluminium Keyboard: emulate PC (Print, Scroll Lock Pause, Num Lock)" it doesn't work.

The keys in question F13, F14 and F15 remain dead functionless keys.

But there are changes going on in the background.
For example the keycode mappings for F13, F14 and F15 do change

With the Tweak Tool Apple Aluminium Keyboard setting un-selected (default)

 $ xmodmap -pke
 keycode 191 = XF86Tools NoSymbol XF86Tools NoSymbol XF86Tools XF86Tools
 keycode 192 = XF86Launch5 NoSymbol XF86Launch5 NoSymbol XF86Launch5 XF86Launch5
 keycode 193 = XF86Launch6 NoSymbol XF86Launch6 NoSymbol XF86Launch6 XF86Launch6

And with Tweak Tool Apple Aluminium Keyboard selected:

 $ xmodmap -pke
 keycode 191 = Print Sys_Req Print Sys_Req Print Sys_Req Print Sys_Req
 keycode 192 = Scroll_Lock NoSymbol Scroll_Lock NoSymbol Scroll_Lock Scroll_Lock
 keycode 193 = Pause Break Pause Break Pause Break Pause Break

So something is happening.