First, let me mention that one of the first things I tested was the fact that the touchscreen was operating during the GUI installation process. Now that we've established that...
After full installation, my touchscreen no longer works at all. I have a Lenovo IdeaPad P400 Touch.
Is there a generic-type driver loaded during the GUI install that gets overwritten after updates/installation possibly? I'm not sure why it sees the device properly (and apparently shows all proper 'statuses' of the device properties), but doesn't work in any way.
Here's what I'm sure you're going to ask to see, and if I can offer any more details at all, please let me know:
xinput list
===========
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ SynPS/2 Synaptics TouchPad id=12 [slave pointer (2)]
⎜ ↳ SYNAPTICS Synaptics Large Touch Screen id=14 [slave pointer (2)]
⎜ ↳ Logitech USB Optical Mouse id=10 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Video Bus id=7 [slave keyboard (3)]
↳ Power Button id=8 [slave keyboard (3)]
↳ Lenovo EasyCamera id=9 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=11 [slave keyboard (3)]
↳ Ideapad extra buttons id=13 [slave keyboard (3)]
xinput list-props 14
====================
Device 'SYNAPTICS Synaptics Large Touch Screen':
Device Enabled (133): 1
Coordinate Transformation Matrix (135): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
Device Accel Profile (261): 0
Device Accel Constant Deceleration (262): 1.000000
Device Accel Adaptive Deceleration (263): 1.000000
Device Accel Velocity Scaling (264): 10.000000
Device Product ID (250): 1739, 7440
Device Node (251): "/dev/input/event12"
Evdev Axis Inversion (265): 0, 0
Evdev Axis Calibration (266): 0, 3132, 0, 1777
Evdev Axes Swap (267): 0
Axis Labels (268): "Abs MT Position X" (331), "Abs MT Position Y" (332), "None" (0), "None" (0)
Button Labels (269): "Button Unknown" (253), "Button Unknown" (253), "Button Unknown" (253), "Button Wheel Up" (139), "Button Wheel Down" (140)
Evdev Middle Button Emulation (270): 0
Evdev Middle Button Timeout (271): 50
Evdev Third Button Emulation (272): 0
Evdev Third Button Emulation Timeout (273): 1000
Evdev Third Button Emulation Button (274): 3
Evdev Third Button Emulation Threshold (275): 20
Evdev Wheel Emulation (276): 0
Evdev Wheel Emulation Axes (277): 0, 0, 4, 5
Evdev Wheel Emulation Inertia (278): 10
Evdev Wheel Emulation Timeout (279): 200
Evdev Wheel Emulation Button (280): 4
Evdev Drag Lock Buttons (281): 0
EDIT (13/05/14): I've definitely discovered that if I, at any point, put my system into any sort of suspension mode ("Suspend" the system), and then awaken it, the touchscreen will begin to work, whereas it was not functioning at all after a cold boot start earlier in the day.
This, in my opinion, appears to point to some of the power functionality causing the problem, as if the drivers need to make a 'call' to wake the device, despite having just been booted fresh.
EDIT (13/05/16): I've submitted a bug report here:
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-evdev/+bug/1180881
