I simply created a new world, got the head from the Creative Tab, and it is displaying the head incorrectly. The Gaia Guardian itself seems unaffected by this issue, although it only renders with a Steve skin.

http://i.imgur.com/yNEsrOH.jpg

• The heads with my skin

http://imgur.com/sX0Trjt

• Gaia Guardian with Steve skin without this issue.

what do you mean by displaying it incorrectly? because the glitchy appearance is intended.

works as intended (checked with 1.7)
the shader gives it the wobbly distortion