Comment 17 for bug 1414930

As a workaround you can force the psmouse driver to use the imps protocol. When using the imps protocol the buttons are mapped correctly. Further, the BIOS option to disable the touchpad is honored.

Of course you can't use the fancy Synaptic touchpad features, but I have no use for them anyway.

$ cat /etc/modprobe.d/psmouse.conf
options psmouse proto=imps

# evtest /dev/input/event5
Input driver version is 1.0.1
Input device ID: bus 0x11 vendor 0x2 product 0x1 version 0x0
Input device name: "PS/2 Synaptics TouchPad"
Supported events:
  Event type 0 (EV_SYN)
  Event type 1 (EV_KEY)
    Event code 272 (BTN_LEFT)
    Event code 273 (BTN_RIGHT)
    Event code 274 (BTN_MIDDLE)
  Event type 2 (EV_REL)
    Event code 0 (REL_X)
    Event code 1 (REL_Y)
Properties:
Testing ... (interrupt to exit)

$ xinput list-props 'PS/2 Synaptics TouchPad'
Device 'PS/2 Synaptics TouchPad':
 Device Enabled (135): 1
 Coordinate Transformation Matrix (137): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
 Device Accel Profile (256): 0
 Device Accel Constant Deceleration (257): 1.000000
 Device Accel Adaptive Deceleration (258): 1.000000
 Device Accel Velocity Scaling (259): 10.000000
 Device Product ID (252): 2, 1
 Device Node (253): "/dev/input/event5"
 Evdev Axis Inversion (260): 0, 0
 Evdev Axes Swap (262): 0
 Axis Labels (263): "Rel X" (145), "Rel Y" (146)
 Button Labels (264): "Button Left" (138), "Button Middle" (139), "Button Right" (140), "Button Wheel Up" (141), "Button Wheel Down" (142), "Button Horiz Wheel Left" (143), "Button Horiz Wheel Right" (144)
 Evdev Middle Button Emulation (265): 0
 Evdev Middle Button Timeout (266): 50
 Evdev Third Button Emulation (267): 0
 Evdev Third Button Emulation Timeout (268): 1000
 Evdev Third Button Emulation Button (269): 3
 Evdev Third Button Emulation Threshold (270): 20
 Evdev Wheel Emulation (271): 1
 Evdev Wheel Emulation Axes (272): 6, 7, 4, 5
 Evdev Wheel Emulation Inertia (273): 10
 Evdev Wheel Emulation Timeout (274): 200
 Evdev Wheel Emulation Button (275): 2
 Evdev Drag Lock Buttons (276): 0