I have the same problem. I thought the output (attached) of synclient
gives interesting insight on this.
I did the following:
1) I started synclient -m 10
2) (time=2.374) I put one finger near the right of the touchpad, trying to keep
the position and pressure constant
3) (approx time=3.931) Keeping the right finger still I put a second finger
near the left side of the touchpad, trying to keep both finger's position and
pressure constant
4) (time=5.296) Keeping the left finger still I release the right finger
5) (time=6.639) I release the left finger
6) I exit synclient
Observable mouse pointer behaviour:
Up to time 3.931 the pointer stays more or less where it is (as expected)
between time 3.931 and 5.296 the pointer moves quickly and erratically all over
the screen (but there seems to be some pattern, the distance and direction from
one position to the next seem rather constant). Occasionally, a left click is
triggered (not sure if it happened during this particular test, sorry). As soon
as I release one finger the pointer stops moving and remains where it is (not
the same place as when I started, of course) until the end of the test.
Some points to note:
- the finger count (column "f") is always reported as 1 although it should give
2 between time 3.931 and time 5.296.
- between time 3.931 and 5.296 (which is when the bug occurs) the x coordinate
sometimes corresponds to the right finger's (around 4620), and the rest of the
time is around the average x coordinate of the two fingers
- between time 3.931 and 5.296 the y coordinate is either at the average
y-coordinate of the two fingers, or the exact value 1741. Twice (time 4.621 and
5.142), the y coordinate becomes *negative* (which never happens when I use a
single finger).
Running xinput list-props "SynPS/2 Synaptics TouchPad" indicates
("Synaptics Capabilities (265): 1, 1, 1, 0, 0") that my synaptics
driver or touchpad doesn't support multi-touch (Although it does under
windows - zooming gestures and all).
My (rather uninformed) guess is that the synaptics driver thinks my
touchpad doesn't support multi-touch, and, when receiving multi-touch
information, tries parsing it as the position of a single finger,
resulting in corrupted information which in turn makes the mouse pointer
jump around.
** Attachment added: "synclient -m 10 output"
http://launchpadlibrarian.net/39273195/syn-out
--
erratic cursor movement with multi touch
https://bugs.launchpad.net/bugs/503944
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