Logitech Marble Trackball scroll not working after upgrade

I’ve done an online upgrade from 13.1 to 13.2, and strangely find that the EmulateWheelButton trick that is necessary to get scroll-wheel type behaviour from this trackball no longer works.
11-evdev.conf looks like this :

Section "InputClass"
    Identifier     "Logitech USB TrackBall"
    MatchProduct   "Marble Mouse (4-button)"
    MatchIsPointer "on"
    Driver         "evdev"
    Option       "Buttons" "9"
    Option         "ButtonMapping" "1 8 3 4 5 6 7 2 9"
    Option         "Device" "/dev/input/by-id/usb-Logitech_USB_Trackball-event-mouse"
    Option         "Emulate3Buttons" "yes"
    Option         "EmulateWheel" "yes"
    Option         "EmulateWheelButton" "8"
    Option         "EmulateWheelInertia" "10" #default 50
    Option         "XAxisMapping" "6 7"
    Option         "ZAxisMapping" "4 5"
EndSection

and Xorg log reports no obvious errors. The mouse works for normal two-button functions but the little button (8) that is supposed to be remapped, continues with its annoying default BrowserBack function
xev reports the expected button numbers, but holding (8) and moving the ball just moves the pointer without generating the button 4 / 5 codes I would expect.
As I say this config worked fine with 13.1, so I’m mighty confused.
Any clues?

That file still owned by root???

Yes - just checked to make sure