Talvez isso também ajude aqui:
Edite o arquivo
/usr/share/X11/xorg.conf.d/50-synaptics.conf
Edite a seção "touchpad catchall" para que fique assim:
Section "InputClass"
Identifier "touchpad catchall"
Driver "synaptics"
MatchIsTouchpad "on"
# This option is recommend on all Linux systems using evdev, but cannot be
# enabled by default. See the following link for details:
# http://who-t.blogspot.com/2010/11/how-to-ignore-configuration-errors.html
MatchDevicePath "/dev/input/event*"
Option "FingerLow" "46"
Option "FingerHigh" "46"
Option "ClickFinger1" "1"
Option "ClickFinger2" "2"
Option "ClickFinger3" "3"
Option "TapButton1" "1"
Option "TapButton2" "2"
Option "TapButton3" "3"
Option "AreaBottomEdge" "85%"
Option "SoftButtonAreas" "60% 0 85% 0 40% 60% 85% 0" # Btn2 LRTB - Btn3 LRTB
Option "EmulateMidButtonTime" "75"
EndSection
(fonte: link )
Experimente algumas das dicas aqui: