Unable to turn off TouchPad

I have a fresh install of qubesos 4.1. I am using i3 window manager.
From dmenu > Mouse and Touchpad screen I turn off the blue slider for SynPS/2 Synaptics TouchPad.

However, after I press “Close”, the TouchPad is still functional. When I navigate back into “Mouse and Touchpad” settings screen, I see that the blue slider for the TouchPad has turned on by itself.

Why is it behaving like this? How can I actually disable TouchPad on my Lenovo Thinkpad X220?