There are fourteen mod files here: one that inserts the left-sided version of the hairstyle for male and female dwarves, elves and humans, a similar file for the right-sided version, and twelve a la carte files with names like "dwarf male right" and "human female left" that insert the left- or right-sided version of the hairstyle for only a particular race/gender combination. Install only one of these files. Installing more than one (even more than one of the a la carte files, which are prima facie non-conflicting) will cause the scalp texture to display incorrectly.
The original bob hairstyle's scalp texture is shared with several other hairstyles. Mostly, this is a nonissue, but the high hairlines of the half-ponytail and braided updo hairstyles expose part of this texture at the corners of the forehead. See below.
The skin and hair colors in these screenshots are the worst case scenario for this effect. It is less visible on characters whose skin and hair colors are similar, and on dark-haired characters in general. This is how it looks on Harding:
My half-ponytail overhaul mostly alleviates this issue for the half-ponytail. Still, I recommend uninstalling this mod if you're not actively using it.
As with other hairstyle mods, your mesh settings must be on Ultra for this mod to display correctly, and it won't display at all in (and may simply crash) the Black Emporium.