Comment 12 for bug 1332384

@Brian,
You could install 3.16 kernel with "sudo apt-get install linux-generic-lts-utopic" command, but I think it's fixed in 3.13 kernel.

After re-tested with newer kernels, I noticed that with the 14.04 stock kernel (3.13.0-24), there is no "Synaptics Touchpad" in xinput output:
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ DLL063E:00 06CB:2934 id=11 [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)]
    ↳ Sleep Button id=9 [slave keyboard (3)]
    ↳ Integrated_Webcam_HD id=10 [slave keyboard (3)]
    ↳ AT Translated Set 2 keyboard id=12 [slave keyboard (3)]
    ↳ Dell WMI hotkeys id=13 [slave keyboard (3)]

"Synaptics Touchpad" will appear with 3.13.0-29, scrolling does not work too.

However, after upgrade to 3.13.0-32 (or use 14.04.1 stock image), scrolling works as expected.
This also applies to the latest update (3.13.0-46 kernel).

Therefore I will close this bug with fix-released.
For those who still affected, please try to run "sudo apt-get dist-upgrade" to upgrade your kernel. Or give 14.04.1 / 14.04.2 a try.
If it's still not working, please feel free to open a new bug with "ubuntu-bug linux" for it.
Thanks!