Additional information, in regards to comment #10: I've updated to a mainline kernel, 3.17-rc5-utopic, and the symptoms are all the same except for one thing: now, whilst holding down the middle-click button, I can also press the right-click button and have it register.
Additional information, in regards to comment #10: I've updated to a mainline kernel, 3.17-rc5-utopic, and the symptoms are all the same except for one thing: now, whilst holding down the middle-click button, I can also press the right-click button and have it register.