Tried with xserver-xorg-input-libinput-hwe-16.04 0.19.0-1ubuntu0.1. No middle button either.
$ xinput set-prop "TPPS/2 IBM TrackPoint" "libinput Button Scrolling Button" 2
X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 131 (XInputExtension)
Minor opcode of failed request: 57 ()
Value in failed request: 0x120
Serial number of failed request: 20
Current serial number in output stream: 21
Tried with xserver- xorg-input- libinput- hwe-16. 04 0.19.0-1ubuntu0.1. No middle button either.
$ xinput set-prop "TPPS/2 IBM TrackPoint" "libinput Button Scrolling Button" 2
X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 131 (XInputExtension)
Minor opcode of failed request: 57 ()
Value in failed request: 0x120
Serial number of failed request: 20
Current serial number in output stream: 21