strange mouse behaviour with xorg

[freenity]

Hi.
My mouse has some strange behaviour with kde and gnome, I think its some
problem with xorg. Anyway the problem is this: when I click left button and
drag it then when I realease it the mouse pointer appears in another
position. It "teleports". I have a PS/2 mouse. Here is the configuration
part of xorg.conf:

Section "InputDevice"
        Identifier  "Mouse0"
        Driver      "mouse"
        Option      "Protocol" "auto"
        Option      "Device" "/dev/sysmouse"
        Option      "ZAxisMapping" "4 5 6 7"
EndSection

Dont know if its important but I have freebsd 6.2 amd64.
Thanks for any help.