Hats seem to convert hairstyles. For most female hairstyles you get the crew cut hairstyle, but for my characters that have the ponytails, they get a "low ponytail" hairstyle while wearing hats instead.
Crew is about right - which looks stupid with a hat.
It's been a problem for a while and since I have spent crowns on hats and they are faulty I am tempted to ask for my crowns back to spend on cosmetics that actually work. But I would rather they actually did a little work and fixed it...
Yeah, this bothers me. If it's any help, some of the hairstyles adjust to the hat, specifically the ones you get with crowns. I know the covenant warlocks and barbaric hair lose some volume to accommodate for the hat. (In fact, the barbaric hair loses length as well and becomes a shoulder-length style). There's a little clipping, depending on the hat, but I think it's a better compromise.
I haven't played around with the various hair styles to see which do and don't get mucked up - primarily I suppose once I design a character I don't tend to want to change the hair, certainly not to accomodate the slacky coding of hats
It's a shame because the last 12 months has seen a couple I'd quite like to wear but my female character ends up looking a little too much like a boy