Can not switch off synaptics touchpad

Binary package hint: xserver-xorg-input-synaptics

Goal: switch off touchpad (as I use a USB mouse)

Case 1:
synaptics is uninstalled or deleted from xorg.conf
=> touchpad keeps working

Case 2:
xserver-xorg-input-synaptics and gsynaptics are installed
xorg.conf is configured properly
touchpad is disabled in gsynaptics
=> touchpad is disabled for a while after boot, but becomes enabled again (randomly) when keyboard is used

Details for Case 2:

Notebook: Albacomp Activa Standard Mobil Traveller V4

Linux: fresh and up-to-date install of Feisty (installed 22/05/2007)

Related packages installed:
xserver-xorg-input-synaptics 0-14-6
gsynaptics 0.9.7-3
linux-image-2.6.20-15-generic 2.6.20-15.27

Related part of /proc/bus/input/devices:
I: Bus=0011 Vendor=0002 Product=0007 Version=0000
N: Name="SynPS/2 Synaptics TouchPad"
P: Phys=isa0060/serio4/input0
S: Sysfs=/class/input/input9
H: Handlers=mouse1 ts1 event9
B: EV=b
B: KEY=6420 0 7000f 0 0 0 0 0 0 0 0
B: ABS=11000003

Related parts of xorg.conf:
Section "InputDevice"
    Identifier "Synaptics Touchpad"
    Driver "synaptics"
    Option "SendCoreEvents" "true"
    Option "Device" "/dev/psaux"
    Option "Protocol" "auto-dev"
    Option "HorizScrollDelta" "0"
    Option "SHMConfig" "on"
EndSection
[...]
Section "ServerLayout"
        Identifier "Default Layout"
        Screen "Default Screen"
        InputDevice "Generic Keyboard"
        InputDevice "Configured Mouse"
        InputDevice "Synaptics Touchpad"
        InputDevice "stylus" "SendCoreEvents"
        InputDevice "cursor" "SendCoreEvents"
        InputDevice "eraser" "SendCoreEvents"
EndSection

Sympthoms:
1. Right after reboot and login the touchpad is disabled (as should be).
The command "synclient -m100" works fine, shows new lines when touchpad is used.
There is nothing new in the output of "dmesg".

2. Using the touchpad and the keyboard simultaniously (especially Home, PgUp, PgDn, End) enables the touchpad.
The command "synclient -m100" does not output new lines, even if the touchpad is used.
The output of "dmesg" is the following:
[ 2503.904000] psmouse.c: bad data from KBC - bad parity
[ 2503.904000] psmouse.c: bad data from KBC - bad parity
[ 2503.904000] psmouse.c: bad data from KBC - bad parity
[ 2503.908000] psmouse.c: bad data from KBC - bad parity
[ 2503.908000] psmouse.c: bad data from KBC - timeout
[ 2503.916000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 4
[ 2503.916000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2503.920000] psmouse.c: bad data from KBC - bad parity
[ 2503.920000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2503.928000] psmouse.c: bad data from KBC - bad parity
[ 2503.932000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 4
[ 2503.932000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2503.932000] psmouse.c: issuing reconnect request
[ 2511.776000] psmouse.c: bad data from KBC - bad parity
[ 2511.776000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2511.776000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2511.780000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2511.780000] psmouse.c: bad data from KBC - bad parity
[ 2511.792000] psmouse.c: bad data from KBC - bad parity
[ 2511.792000] psmouse.c: TouchPad at isa0060/serio4/input0 - driver resynched.
[ 2511.812000] psmouse.c: bad data from KBC - bad parity
[ 2511.812000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 4
[ 2511.816000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2511.816000] psmouse.c: bad data from KBC - bad parity
[ 2511.824000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2511.828000] psmouse.c: TouchPad at isa0060/serio4/input0 - driver resynched.
[ 2516.936000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2516.936000] psmouse.c: bad data from KBC - bad parity
[ 2516.936000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2516.940000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2516.948000] psmouse.c: bad data from KBC - bad parity
[ 2516.956000] psmouse.c: TouchPad at isa0060/serio4/input0 - driver resynched.
[ 2516.968000] psmouse.c: bad data from KBC - bad parity
[ 2516.968000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2516.972000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2516.972000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2516.972000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2516.976000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2516.976000] psmouse.c: issuing reconnect request
[ 2520.024000] psmouse.c: bad data from KBC - bad parity
[ 2520.028000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 4
[ 2520.028000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2520.040000] psmouse.c: bad data from KBC - bad parity
[ 2520.040000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 4
[ 2520.044000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 1
[ 2520.060000] psmouse.c: bad data from KBC - bad parity
[ 2520.064000] psmouse.c: TouchPad at isa0060/serio4/input0 lost sync at byte 4
[ 2520.064000] psmouse.c: issuing reconnect request
[ 2520.996000] Synaptics Touchpad, model: 1, fw: 6.3, id: 0x81a0b1, caps: 0xa04713/0x204000
[ 2521.032000] input: SynPS/2 Synaptics TouchPad as /class/input/input9

Thank you for your help!