I think you can add Option "SHMConfig" "true to /usr/share/X11/xorg.conf.d/50-synaptics.conf which may look like this:

Section "InputClass"

     Identifier "touchpad catchall"

     Driver "synaptics"

     MatchIsTouchpad "on"

     MatchDevicePath "/dev/input/event*"

           Option "TapButton1" "1"

           Option "TapButton2" "2"

           Option "TapButton3" "3"

           Option "SHMConfig"  "true"

EndSection

Or temporarily you can do synclient SHMConfig=1 in terminal to check the behaviour you want.