Quote Originally Posted by Iscah View Post
I would guess that possibly having the "hat" visible, even if it's just a nose, might trigger the hair to do something strange that they want to avoid happening.
Funnily enough, there is an example of this happening, though it might've been fixed since it was discovered. The Hempen Coif and all hats sharing the same model would not appear when worn by a Viera, but toggling your helmet on while wearing one (or a hat glamoured to look like one) would disable your hair physics.