Misspelling names deliberately. Is it rude?

I have a question based on a huge pet peeve of mine and I think it could be controversial in that people's feelings on the issue probably vary.

If you send someone an email in a professional setting and your name is right there in your signature line, do you find it rude if the person replies and spells your name completely differently than the way you actually spell it? It's not as if they can't see how it's spelled.

Is it a lack of attention? Are they in a hurry? They just don't care? What leads people to do this and does it bother you?