Comment 9 for bug 1694225

I'm not sure why but a workaround is to run:

sudo rmmod psmouse && sudo modprobe psmouse proto=imps

Then the touchpad gets recognized as:

I: Bus=0011 Vendor=0002 Product=0001 Version=0000
N: Name="PS/2 Synaptics TouchPad"
P: Phys=isa0060/serio1/input0
S: Sysfs=/devices/platform/i8042/serio1/input/input19
U: Uniq=
H: Handlers=mouse0 event4
B: PROP=1
B: EV=7
B: KEY=70000 0 0 0 0
B: REL=3

This prevents the lock effect from happening.