Comment 34 for bug 132627

Fixed in Jaunty adding
Option "SHMConfig" "true"
as the last line of Section "InputDevice"
############################
Section "InputDevice"
    Identifier "Synaptics Touchpad"
    Driver "synaptics"
    Option "SendCoreEvents" "true"
    Option "Device" "/dev/psaux"
    Option "Protocol" "auto-dev"
    Option "HorizScrollDelta" "0"
    Option "SHMConfig" "true"
EndSection
############################

Moving Section "InputDevice" Identifier "Configured Mouse", i.e. my USB mouse, after Synaptics Touchpad

And finally adding InputDevice "Synaptics Touchpad" in Section "ServerLayout"

############################
Section "ServerLayout"
    Identifier "Default Layout"
    Screen "Default Screen" 0 0
    InputDevice "Keyboard0" "CoreKeyboard"
    InputDevice "Configured Mouse"
    InputDevice "Synaptics Touchpad"
EndSection