Hi,
Here is a test script I came up with based on your description. It creates an avatar that is scaled along the x-axis and adds a custom head to it. I don't notice any problems. Can you try running it and telling me if you notice the problem with it? If not, can you supply a simple script that reproduces the issue?
Code:
import viz
viz.go()
s=1.4
face = viz.add('biohead_talk.vzf',scale=(s,s,s))
model = viz.add('male.cfg',pos=(0,0,5),euler=(180,0,0),scale=(2,1,1))
model.setFace(face)
model.state(12)