I always figured it was an engine related bug. Whenever the refraction effect is on it'll remove your character's hair. If you're wearing a helmet that takes up the hair slot everything seems to work fine. For whatever reason, the hair will attach itself to pipboys and weapons, or even create a big refracted shape glitch all over the place. Maybe an amendment to the stealth effect could fix it? Something that'll fill in the hair slot (if it is 'empty', so it doesn't override any helmets you want to wear) whenever the stealth effect is active. Maybe?