See DaveS and my replies here - I think you may be running into similar issues.
I'd also rename your "Head and ears" layer to something without "head" so it doesn't get accidentally tagged as another head.
Thanks for the reply. I looked through the thread and tried to apply the necessary changes, but I'm afraid I'm just not quite getting it. Here's a picture of the changes I made:
All of the facial features respond, but the keyboard command to switch the head movement just isn't working for me. Can you tell me how I should be labeling the Left/Right Quarter bins? I don't have front or profile layers built. Do you think this might be the problem?
I finally figured out that it was a case of labeling my left/right quarter layers wrong: they were associated with the character's left/ right instead of the animator's. Once I switched the name, it started to work perfectly. Proves that the small things really make a difference.
Thank you for all of your help oksamurai!