SUMMARY:
When using a external monitor with a touchscreen, the physical range of the touchscreen input is mapped to the total pixel range of both monitors combined. I have a 1920x1080 external monitor with a touchscreen extended to the left of my 1366x768 laptop screen. When my finger is on the top left corner of the external monitor, the mouse is under my finger (as it should be). However as I move my finger to the right, the mouse accelerates in front of my finger. Once my finger touches the right bezel, the mouse is at right most edge of my laptop screen. Likewise this happens in the vertical axis, however the effect is "clipped" when the mouse is on the laptop screen due to the resolution difference and the top edge alignment.

I have tried this monitor on a windows machine and it does not act this way.

If I unify the displays the touchscreen acts as expected.

STEPS TO REPRODUCE
1. Use external monitor with touchscreen

OBSERVED RESULT
Mouse not tracking finger but rather it is mapped to the combined pixel dimensions of the two monitors.

EXPECTED RESULT
The mouse should be under the finger input at all times.

SOFTWARE/OS VERSIONS
Windows: 10 (For the Windows PC that confirmed that this is a software bug, not hardware)
MacOS: N/A
Linux/KDE Plasma: Neon Stable Developer Edition
(available in About System)
KDE Plasma Version: 5.14.3
KDE Frameworks Version: 5.53.0
Qt Version: 5.11.2

ADDITIONAL INFORMATION
The windows PC, was coincidentally the same laptop as my machine.

Laptop:
Dell Latitude E7240

If needed, I can attach a screen capture of the behaviour in case my description is not clear