Never had anyone do this to me, but it happened to my best friend. SHe had an awesomely unique character and one person completely copied it. I mean the bio was the same, the name, the clan, and the look. THe only difference was that the new person had a face mane. She almost started crying when the person came up to her and started yelling at her. Note she's had the character for nearly three months at this point, everything in her bio happened.
This person obviously stole her character. She didn't even pick the second half of her name, the rp leader did. That was irritating, but something I think is true is that someone can take your character's looks, their name, their history, but only YOU know how to play them accurately, and so they are yours no matter what.