Yes, I was recently told in no uncertain terms that a character who is always called by a nickname is "really" named Letitia. After I explained why I called her something else in my fic, the response was that we should keep calling her by her nickname in the series (because we don't know what her "real" name is?), despite the fact that for many reasons it's an inappropriate nickname for an adult. Sigh.

On the other hand, sometimes I do think that a writer really has a character WRONG. In which case I don't say anything about it, because why?