Ubuntu – 14.04 ThinkPad Edge volume buttons stopped working

The media buttons for increasing/decreasing the volume of audio output and the mute-button stopped working out of nowhere. The buttons are still recognized by the system, as I can select them to perform the desired action in the gnome control centre, but pressing on of these buttons will do nothing. All the other buttons of the fn-row are working properly.

xev says on button-press:

KeyPress event, serial 37, synthetic NO, window 0x4600001,
root 0x9d, subw 0x0, time 190010, (19,-11), root:(1244,41),
state 0x0, keycode 122 (keysym 0x1008ff11, XF86AudioLowerVolume), same_screen YES,
XLookupString gives 0 bytes: 
XmbLookupString gives 0 bytes: 
XFilterEvent returns: False

KeyRelease event, serial 37, synthetic NO, window 0x4600001,
root 0x9d, subw 0x0, time 190104, (19,-11), root:(1244,41),
state 0x0, keycode 122 (keysym 0x1008ff11, XF86AudioLowerVolume), same_screen YES,
XLookupString gives 0 bytes: 
XFilterEvent returns: False

KeyPress event, serial 37, synthetic NO, window 0x4600001,
root 0x9d, subw 0x0, time 191040, (19,-11), root:(1244,41),
state 0x0, keycode 123 (keysym 0x1008ff13, XF86AudioRaiseVolume), same_screen YES,
XLookupString gives 0 bytes: 
XmbLookupString gives 0 bytes: 
XFilterEvent returns: False

KeyRelease event, serial 37, synthetic NO, window 0x4600001,
root 0x9d, subw 0x0, time 191118, (19,-11), root:(1244,41),
state 0x0, keycode 123 (keysym 0x1008ff13, XF86AudioRaiseVolume), same_screen YES,
XLookupString gives 0 bytes: 
XFilterEvent returns: False

What can I do to get them working again?

EDIT: Ok, so I tried to create a shortcut for "Volume up", using the command pactl set-sink-volume 0 +10%. Binding it to Strg++ worked, but binding it to the "Volume up"-Button has no effect.