I am also affected (Kubuntu 12.04 32-bit), but diffently I guess.

* xserver-xorg installed packages :

ii  xserver-xorg                    1:7.6+12ubuntu1                 X.Org X server
ii  xserver-xorg-core               2:1.11.4-0ubuntu10.1            Xorg X server - core server
ii  xserver-xorg-input-evdev        1:2.7.0-0ubuntu1                X.Org X server -- evdev input driver

when I plug the headset, the x session quits and I am back to the graphical login interface (kdm).
if I leave the headser plugged, then the x server freeze completly.

I run evtest and obtain what follows :

Available devices:
/dev/input/event0:      Lid Switch
/dev/input/event1:      Power Button
/dev/input/event10:     HDA Intel Headphone
/dev/input/event11:     SynPS/2 Synaptics TouchPad
/dev/input/event2:      Sleep Button
/dev/input/event3:      Power Button
/dev/input/event4:      AT Translated Set 2 keyboard
/dev/input/event5:      Video Bus
/dev/input/event6:      Logitech Unifying Device. Wireless PID:4017
/dev/input/event7:      HDA Intel Rear Mic
/dev/input/event8:      HDA Intel Front Mic
/dev/input/event9:      HDA Intel Front Headphone
Select the device event number [0-11]: ^C

the Xorg log indicates the use of event12 :

[  3319.281] (II) config/udev: Adding input device Logitech Unifying Device. Wireless PID:4017 (/dev/input/event6)
[  3319.281] (**) Logitech Unifying Device. Wireless PID:4017: Applying InputClass "evdev pointer catchall"
[  3319.281] (II) Using input driver 'evdev' for 'Logitech Unifying Device. Wireless PID:4017'
[  3319.281] (II) Loading /usr/lib/xorg/modules/input/evdev_drv.so
[  3319.281] (**) Logitech Unifying Device. Wireless PID:4017: always reports core events
[  3319.281] (**) evdev: Logitech Unifying Device. Wireless PID:4017: Device: "/dev/input/event6"
[  3319.281] (--) evdev: Logitech Unifying Device. Wireless PID:4017: Vendor 0x46d Product 0xc52b
[  3319.281] (--) evdev: Logitech Unifying Device. Wireless PID:4017: Found 20 mouse buttons
[  3319.281] (--) evdev: Logitech Unifying Device. Wireless PID:4017: Found scroll wheel(s)
[  3319.281] (--) evdev: Logitech Unifying Device. Wireless PID:4017: Found relative axes
[  3319.281] (--) evdev: Logitech Unifying Device. Wireless PID:4017: Found x and y relative axes
[  3319.281] (II) evdev: Logitech Unifying Device. Wireless PID:4017: Configuring as mouse
[  3319.281] (II) evdev: Logitech Unifying Device. Wireless PID:4017: Adding scrollwheel support
[  3319.281] (**) evdev: Logitech Unifying Device. Wireless PID:4017: YAxisMapping: buttons 4 and 5
[  3319.281] (**) evdev: Logitech Unifying Device. Wireless PID:4017: EmulateWheelButton: 4, EmulateWheelInertia: 10, EmulateWheelTimeout: 200
[  3319.281] (**) Option "config_info" "udev:/sys/devices/pci0000:00/0000:00:1d.0/usb6/6-1/6-1:1.2/0003:046D:C52B.0003/input/input6/event6"
[  3319.281] (II) XINPUT: Adding extended input device "Logitech Unifying Device. Wireless PID:4017" (type: MOUSE, id 10)
[  3319.281] (II) evdev: Logitech Unifying Device. Wireless PID:4017: initialized for relative axes.
[  3319.282] (**) Logitech Unifying Device. Wireless PID:4017: (accel) keeping acceleration scheme 1
[  3319.282] (**) Logitech Unifying Device. Wireless PID:4017: (accel) acceleration profile 0
[  3319.282] (**) Logitech Unifying Device. Wireless PID:4017: (accel) acceleration factor: 2.000
[  3319.282] (**) Logitech Unifying Device. Wireless PID:4017: (accel) acceleration threshold: 4
[  3319.282] (II) config/udev: Adding input device Logitech Unifying Device. Wireless PID:4017 (/dev/input/mouse0)
[  3319.282] (II) No input driver specified, ignoring this device.
[  3319.282] (II) This device may have been added with another device file.
[  3319.282] (II) config/udev: Adding input device Logitech Logitech Wireless Headset (/dev/input/event12)
[  3319.282] (**) Logitech Logitech Wireless Headset: Applying InputClass "evdev keyboard catchall"
[  3319.282] (II) Using input driver 'evdev' for 'Logitech Logitech Wireless Headset'
[  3319.282] (II) Loading /usr/lib/xorg/modules/input/evdev_drv.so
[  3319.282] (**) Logitech Logitech Wireless Headset: always reports core events
[  3319.282] (**) evdev: Logitech Logitech Wireless Headset: Device: "/dev/input/event12"
[  3319.282] (--) evdev: Logitech Logitech Wireless Headset: Vendor 0x46d Product 0xa29
[  3319.282] (--) evdev: Logitech Logitech Wireless Headset: Found absolute axes
[  3319.282] (--) evdev: Logitech Logitech Wireless Headset: Found absolute multitouch axes
[  3319.282] (--) evdev: Logitech Logitech Wireless Headset: Found keys
[  3319.282] (II) evdev: Logitech Logitech Wireless Headset: Configuring as mouse
[  3319.282] (II) evdev: Logitech Logitech Wireless Headset: Configuring as keyboard
[  3319.282] (**) Option "config_info" "udev:/sys/devices/pci0000:00/0000:00:1d.1/usb7/7-1/7-1:1.3/input/input13/event12"
[  3319.282] (II) XINPUT: Adding extended input device "Logitech Logitech Wireless Headset" (type: KEYBOARD, id 11)
[  3319.282] (**) Option "xkb_rules" "evdev"
[  3319.282] (**) Option "xkb_model" "pc105"
[  3319.282] (**) Option "xkb_layout" "fr"
[  3319.282] (**) Option "xkb_variant" "oss"
[  3319.283] (II) evdev: Logitech Logitech Wireless Headset: initialized for absolute axes.

Is it related with the ABI problem you pointed ?