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I'm on a Dell Latitude E7240 running 12.04 LTS and my touch pad acts erratically. It happens because my middle and ring fingers accidentally touch the top edge of the pad while my pointer finger is moving the cursor. I can reproduce this on purpose by running "xinput --test [device number]" and watching the events while I do the following:
- Touch the pad near the middle or bottom. The cursor moves slightly as my finger wiggles around.
- Without removing the first finger, touch the pad again with a second finger above the first finger. The cursor shoots up to a[1]=0 (which is the y position).
- Without removing the first finger, remove the second (top) finger. The cursor shoots back down to a[1]=<some large number> Sometimes it takes it all the way to the bottom of the screen, sometimes it goes back to where it was, or somewhere else. I haven't been able to figure out how it decides what to go back to.

With this, while I touching with my pointer finger and my middle or ring
finger accidentally touch the pad at the top, the cursor shoots where I
don't want it. Then when my middle/ring finger leaves the pad (usually
because I started cursing (get it?) at my cursor), it shoots back down
again somewhere completely arbitrary.

Similarly:
- Touch the bad near the top.
- Without removing the top finger, touch somewhere near the bottom. The cursor doesn't (yet) move.
- Lift the top finger. The cursor shoots to the bottom.
- Put down the top finger again, without lifting the bottom. The cursor shoots back up again.

You can make the cursor shoot up and down just by keeping your bottom
finger down and tapping the top finger. The cursor follows the top
finger no matter what you do.

Interestingly, this does NOT happen from side-to-side. Two touches side-
by-side trigger the multi-touch gestures and don't move the cursor.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: linux-image-3.13.0-29-generic 3.13.0-29.53~precise1
ProcVersionSignature: Ubuntu 3.13.0-29.53~precise1-generic 3.13.11.2
Uname: Linux 3.13.0-29-generic x86_64
ApportVersion: 2.0.1-0ubuntu17.6
Architecture: amd64
Date: Mon Jun  9 16:59:49 2014
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 SHELL=/bin/bash
SourcePackage: linux-lts-trusty
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete


** Tags: amd64 apport-bug precise running-unity
-- 
Alps Touchpad acts erratically when multi-touch is vertical, not horizontal
https://bugs.launchpad.net/bugs/1328313
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