Bug 433378

SUMMARY

I use a laptop (Dell Inspiron 14 2in1) that has a tocuhcreen with active pen. I have KDE Neon. While debugging a problem in touchegg (https://github.com/JoseExposito/touchegg/issues/458) I stumbled upon the possible reason for this bug: when I touch the screen and then use the pen i get "ghost tocuhes" that makes the use of the touchscreen impossible until I disable and re-enable the corresponding input device with xinput.

STEPS TO REPRODUCE
1. Touch the screen with one finger.
2. USe the pen on the screen (even just close enouch to trigger proximity)
3. Take the finger off the screen, now there is a ghost touch and the cursor will not follow your touch anymore

ADDITIONAL INFO

The debugging of touchegg led me to use libinput debug-events to monitor libinput since there is no native gesture support. This gets me to believe that KDE for some reason do not use the (correctly reported) TOUCH_CANCEL event that occur after the pen gets in proximity of the panel.
I tried installing gnome-shell to see if the problem is not on KDE but on X and in gnome it seems to work correctly.


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE Neon
(available in About System)
KDE Plasma Version: 5.21.0
KDE Frameworks Version: 7.79.0
Qt Version: 5.15.2