Thanks it appears harmless, this is 4.2.1 compiled on alpha box.
XF86Config settings:
Section "InputDevice"

# Identifier and driver

    Identifier  "Mouse1"
    Driver      "mouse"
    Option "Protocol"    "wsmouse"
    Option "Device"      "/dev/wsmouse0"
EndSection
-Mel


Stephen Ma wrote:

> mel> How do i fix this in mouse settings of XF86Config file
>
> Matthias> I've never seen an error like this.
>
> I've seen it a few times on a couple of machines, but in all cases, it
> always seems to be harmless. As far as I can tell, it's caused by a
> botch somewhere in the reading of wsmouse events that causes the X
> server to be out of sync with the wsmouse device.
>
> - S