Disable scroll wheel horizontal buttons (back/forward)

I have a problem, it's driving me insane: Recently got a Logitech M500:

Bus 002 Device 004: ID 046d:c069 Logitech, Inc. M500 Laser Mouse

It has nine buttons that I can identify:

• Two on the left side


• Left, right


• Wheel press


• Wheel scroll up, wheel scroll down


• Wheel press left, wheel press right

The last two are driving me insane. Every time I try to click the wheel, I accidently hit the "wheel press left" button and Firefox goes to the last visited page. It is annoying as hell.

Easy enough, right? Just find out which buttons xev shows and disable them. Wrong! xev does not generate "ButtonPress/ButtonRelease" events, but strange "LeaveNotify/EnterNotify/KeymapNotify" pairs:

 LeaveNotify event, serial 40, synthetic NO, window 0x4a00001,
    root 0x94, subw 0x0, time 2344319, (104,86), root:(113,207),
    mode NotifyGrab, detail NotifyAncestor, same_screen YES,
    focus YES, state 0

EnterNotify event, serial 40, synthetic NO, window 0x4a00001,
    root 0x94, subw 0x0, time 2344319, (104,86), root:(113,207),
    mode NotifyUngrab, detail NotifyAncestor, same_screen YES,
    focus YES, state 0

KeymapNotify event, serial 40, synthetic NO, window 0x0,
    keys:  4294967188 0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   

Now surely, the 4294967188 (-108 in twos complement as 32 bit integer if that helps) will be the keycode, right? Wrong again! It's the same number for both the horizontal wheel left/right and the side back/front buttons.

Here's my xinput list of the device:

Logitech USB Laser Mouse                    id=15   [slave  pointer  (2)]
    Reporting 7 classes:
        Class originated from: 15. Type: XIButtonClass
        Buttons supported: 16
        Button labels: "Button Left" "Button Middle" "Button Right" "Button Wheel Up" "Button Wheel Down" "Button Horiz Wheel Left" "Button Horiz Wheel Right" "Button Side" "Button Extra" "Button Forward" "Button Back" "Button Task" "Button Unknown" "Button Unknown" "Button Unknown" "Button Unknown"
        Button state:
        Class originated from: 15. Type: XIValuatorClass
        Detail for Valuator 0:
          Label: Rel X
          Range: -1.000000 - -1.000000
          Resolution: 1 units/m
          Mode: relative
        Class originated from: 15. Type: XIValuatorClass
        Detail for Valuator 1:
          Label: Rel Y
          Range: -1.000000 - -1.000000
          Resolution: 1 units/m
          Mode: relative
        Class originated from: 15. Type: XIValuatorClass
        Detail for Valuator 2:
          Label: Rel Horiz Wheel
          Range: -1.000000 - -1.000000
          Resolution: 1 units/m
          Mode: relative
        Class originated from: 15. Type: XIValuatorClass
        Detail for Valuator 3:
          Label: Rel Vert Wheel
          Range: -1.000000 - -1.000000
          Resolution: 1 units/m
          Mode: relative
        Class originated from: 15. Type: XIScrollClass
        Scroll info for Valuator 2
          type: 2 (horizontal)
          increment: 1.000000
          flags: 0x0
        Class originated from: 15. Type: XIScrollClass
        Scroll info for Valuator 3
          type: 1 (vertical)
          increment: -1.000000
          flags: 0x2 ( preferred )

It appears to map the buttons just as they normally would be. So what happens when I write a small script that calls "xinput query-state $DEVNO" in a loop and press the horrible buttons? You guessed it:

2 classes :
ButtonClass
    button[1]=up
    button[2]=up
    button[3]=up
    button[4]=up
    button[5]=up
    button[6]=up
    button[7]=up
    button[8]=up
    button[9]=up
    button[10]=up
    button[11]=up
    button[12]=up
    button[13]=up
    button[14]=up
    button[15]=up
    button[16]=up
ValuatorClass Mode=Relative Proximity=In
    valuator[0]=538
    valuator[1]=456
    valuator[2]=-2
    valuator[3]=-464

They always show up as "up" although they're clearly "down". Mouse buttons that do generate proper ButtonPress events (left/right for example) do show up ad "down" like they should.

Please help me with this, I'm going to smash this fucking mouse to pieces otherwise!

Thank you so much Jonas