Comment # 4 on bug 1161298 from Vitaly Bakulev

(In reply to Takashi Iwai from comment #3)
> Maybe another input device gives the key event for the corresponding keys? 
> That would explain why multiple events are seen by showkey.
> So, please examine all input devices.
> 
> The hwinfo is needed in anyway for identifying the systems and for more
> comprehensive checks.

Evtest shows volume up/down events registered by:
/dev/input/event0:    AT Translated Set 2 keyboard
/dev/input/event7:    Intel HID 5 button array
Does it mean that they both handle them each time and thus produce double
input?

This input device claims to be able to handle them, but does not give actual
output like the two above do:
/dev/input/event6:    Intel HID events

I am attaching hwinfo to the bug.