tangential pressure stuck on Intuos 3

[ec1oud]

I have a PTZ-630 with several styli, including an airbrush. The airbrush tangential pressure seems to get stuck at one value, maybe the first value that it saw after the tablet has been plugged in and the stylus comes into proximity, or something like that.

It still works fine on wayland, so the hardware is OK and libinput is ok.

I mostly take care of the wacom support in Qt, and this is the line where it's reading tangential pressure on X11:

https://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp#n1650

It's possible there is some new bug in this Qt plugin, but I doubt it. I've been testing it often enough over the years.

When running xinput test I don't see any numbers changing in response to the movement of the tangential pressure thumbwheel.

How do I know it's this driver:

$ grep Using ~/.local/share/xorg/Xorg.0.log
...
[339182.728] (II) Using input driver 'wacom' for 'Wacom Intuos3 6x8 Pad'
[339182.785] (II) Using input driver 'wacom' for 'Wacom Intuos3 6x8 Pen'
[339182.787] (II) Using input driver 'wacom' for 'Wacom Intuos3 6x8 Pen eraser'
[339182.788] (II) Using input driver 'wacom' for 'Wacom Intuos3 6x8 Pen cursor'

If I switch to libinput in my /etc/X11/xorg.conf.d/99-wacom.conf it doesn't even distinguish the airbrush from a regular stylus. So the wacom driver still needs to be kept working.

I have Arch Linux so the version we're talking about is 1.6.4-2; libxi version is 1.8.2-1.