Comment 27 for bug 51537

prokher, that is a different issue. In this case, the buttons are handled incorrectly, while your case, it's not detected at all. You should be looking at bug #217504 https://bugs.launchpad.net/bugs/217504

On another note, interestingly, after reinstalling alsa, my buttons work correctly, even without the patch. It doesn't appear to be an artifact from the above bug, as xev detects it, I get an OSD, and I can rebind the key.