Not a bug, this has happened to me before. The symbols sometimes read as the same character and it'll tell you that the name is already in use if you try changing just the symbol at one time. Change his entire name to something different without a symbol, then change it back to his original name you want.

I tried what you suggested and it didn't work. A bunch of other names work just fine with the symbol...but Smoking Gun just won't work. Neither will the name Gunsmoke. I tried "A Smoking Gun" and that worked. I'm not entirely satisfied with that name, but I suppose it will do.