Mhmm, this has happened to me. Well, my friend rather. She had wolf character named, "Sahara." Well, that's the name of a desert so I say it is probably pretty common. Well, we were at Cape and talking in local then suddenly, this highlighter feline with the name Sahara F or just Sahara, I can't remember, comes up and starts yelling. "SAHARA IS MY NAME!!!" And we both just told her it wasn't her name; it could be anyone's name, not just hers. But she continued. "No! Change your name to something else! Sahara is my name and I've had it forever! It's the only name I use!!!" And my friend and I basically just ignored her from that point on. Honestly. She did not come up with that name!
And to be honest, can any of us really claim a name? We don't own the alphabet. We can't claim it or letters we use from it. I understand if you have the name of a group that is entirely made up by you, or a character name you made up, and someone has the same exact spelling for it, that it could be considered name stealing. But in the end, like I said, no one owns the alphabet.