May 10 2016
This is a duplicate.
I up voted the old one.
Same as ticket: 13406
Same as Ticket 0013399
Having the exact same issue.
It feels like I'm deaf in the right ear.
Hadn't noticed it until playing the campaign.
May 9 2016
I too have recently discovered that several buttons are unusable.
Here's to hoping they get it fixed.
Edit: By modifying the config file I was able to get buttons past 16 mapped.
Unfortunately they don't seem to work.
See uploaded image for reference.
I will mess around some more.