I've noticed quite a few problems using the camera with a full (and dark color) beard. This causes two problems.
First, the software seems to confuse my mouth and my beard hair.
Second, the software can't recognize the bottom of my chin. This makes sense, but it keeps jumping from the bottom of my mouth to the bottom of the beard. This tricks the software into thinking that I'm rapidly moving towards and away from the camera. This could be fixed by using eye and nose tracking to triangulate the position and calculate the scale of the face in relation to the sides of the head.
I really enjoy having an epic beard and don't want to shave it so I can use this software to its fullest.