Mouse movement jerky after plugging in external monitor

[Richard W.M. Jones]

I have a Lenovo X230 (laptop with a small internal screen) and
a large external screen.

When the external screen is not plugged in, mouse movements are
fine.

When I plug in the external screen (I have the XFCE desktop spread
over both internal and external), horizontal movements of the mouse
become quite "jerky".  It seems to move in minimum units of around 10
pixels.

It's almost as if mouse movements are being calculated as a percentage
of the screen width.

I can't find anything about this via searching.  Anyone have any ideas?

Rich.

Fedora 18
/var/log/Xorg.0.log attached

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Fedora Windows cross-compiler. Compile Windows programs, test, and
build Windows installers. Over 100 libraries supported.
http://fedoraproject.org/wiki/MinGW