I have run into this myself then editing textures, generally it happens if you have material groups with transparency and no texture or transparency map.

Example is if you try to hide part of the hair like the bangs, first advice is to look over all material groups for the hair and see if any of them looks different, in this case just give them the same material settings as the other ones.

One workaround is to change the display style for the hair under display and element.