Why Visual Studio UML Editor shows 1:1 relationship as two directional one to many relationships

Question

I have a class:

  //ClientCard
 public class KartaKlienta {
        [Required]
        public virtual Klient Wlasciciel { get; set; } //Owner
    }

and

  //Client
 public class Klient : Osoba {
        public virtual KartaKlienta KartaKlienta { get; set; } //ClientCard
    }

I generated Uml diagram and to my surprise it shows 2 one to many relationships: http://s4.postimg.org/iam36ol8d/stack.png ( I can't add picture, as I have less than 10 reputation)

Why it doesn't show sing one to one relationship?