MSFT Wireless Notebook Laser Mouse 6000 versus FC3

[esculent]

I just bought a MSFT Wireless Notebook Laser Mouse 6000 (a USB mouse) to replace another model of MSFT USB compact wireless notebook mouse that broke. The old one worked fine with my FC3 desktop system through a USB KVM switch. But the new one seems to generate mouse button #2 ("middle mouse button") press/release events every time I move the mouse. This makes it very hard to type, copy/paste, select windows, etc.

The new mouse works fine when connected to a notebook running Windows, just as the old one did. I've tried fiddling with /etc/X11/xorg.conf, which now says in part

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/input/mice"
Option "Buttons" "3"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "no"
EndSection

I have tried all combinations of Emulate3Buttons = yes, no; Buttons = 3, 4, 5; and commenting out the ZAxisMapping line or leaving it in. I restart X with ctrl-alt-backspace after each change, but the mouse continued to act in the same weird way after each change.

Xorg.0.log contains these entries (edited):

(**) Option "Protocol" "IMPS/2"
(**) Mouse0: Device: "/dev/input/mice"
(**) Mouse0: Protocol: "IMPS/2"
(**) Option "CorePointer"
(**) Mouse0: Core Pointer
(**) Option "Device" "/dev/input/mice"
(**) Option "Buttons" "3"
(**) Option "Emulate3Buttons" "no"
(**) Mouse0: Buttons: 3
[snip]
(II) XINPUT: Adding extended input device "Keyboard0" (type: KEYBOARD)
(II) XINPUT: Adding extended input device "Mouse0" (type: MOUSE)
(II) Mouse0: ps2EnableDataReporting: succeeded

Any suggestions?