Unwanted touchpad movements on tap with Synaptics touchpad on DELL Inspiron-3521

https://gitlab.freedesktop.org/libinput/libinput/issues/199

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When using the touchpad, the mouse cursor moves even when keeping the finger still on one point.

Triggering the behaviour: this happens when the contact surface is very small, so it gets triggered for example when tapping on a button, right before the finger leaves the touchpad. This makes clicking buttons using the touchpad (for example, the "x" button in the browser tabs) very difficult.

In attachment, an evemu-record done keeping the finger on one point, barely touching the touchpad.

The recording was done with the command:

sudo evemu-record > touchpad.evemu
Available devices:
/dev/input/event0: Power Button
/dev/input/event1: Lid Switch
/dev/input/event2: Power Button
/dev/input/event3: AT Translated Set 2 keyboard
/dev/input/event4: Video Bus
/dev/input/event8: SynPS/2 Synaptics TouchPad
/dev/input/event9: Dell WMI hotkeys
/dev/input/event10: HDA Intel PCH Mic
/dev/input/event11: HDA Intel PCH Front Headphone
/dev/input/event12: HDA Intel PCH HDMI/DP,pcm=3
/dev/input/event13: Laptop_Integrated_Webcam_HD: In
Select the device event number [0-13]: 8

To replay the recording (the strange behaviour is particularly visible in the final part):

sudo evemu-play /dev/input/event8 < touchpad.evemu

(replace event8 with your input device)

System info:

lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic

apt-cache policy libinput10
libinput10:
  Installato: 1.10.4-1
  Candidato: 1.10.4-1
  Tabella versione:
 *** 1.10.4-1 500
        500 http://it.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
        100 /var/lib/dpkg/status

apt-cache policy libinput-bin
libinput-bin:
  Installato: 1.10.4-1
  Candidato: 1.10.4-1
  Tabella versione:
 *** 1.10.4-1 500
        500 http://it.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
        100 /var/lib/dpkg/status