Entity Framework 6 code first fluent API one to one relation with both ends required

I want to implement One to One relation with both ends required with the fluent API in Entity Framework 6 code first.

I have the principal class:

public class Student
{
    public int Id{ get;  set;} 
    public string Name{ get;  set;}
    public StudentProfile StudentProfile { get; set; } 
}

and I have the dependent class:

public class StudentProfile
{
    public int Id{ get;  set;} 
    public string Description{ get;  set;}
    public Student Student { get; set; } 
}

Additionally, I have the configuration for the relation one to one, in this case both ends ARE REQUIRED:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Student>()
            .HasRequired(student => student.StudentProfile)
            .WithRequiredPrincipal(profile => profile.Student);

     base.OnModelCreating(modelBuilder);   
}

After executing update-database, the resulting generated tables are:

The table StudentProfile columns:

The table Students columns:

On the Main program, I am able to save a Student with its profile:

 UMLModel umlContext = new UMLModel();

 //Studentprofile object
 StudentProfile studentProfile = new StudentProfile();
 studentProfile.Description = "Emily Profile Description";

 //Student object
 Student student = new Student();
 student.Name = "Emily";
 student.StudentProfile = studentProfile;

 //Save Student and StudenProfile Objects
 umlContext.Students.Add(student);
 umlContext.SaveChanges();

Once executed the Main program,on the database,the StudentProfiles table is:

and the Students table is:

The problem becomes when I try to save one student WITHOUT its profile, the program allows to save it and it is supposed to not allow it:

UMLModel umlContext = new UMLModel();

Student student = new Student();
student.Name = "John";

umlContext.Students.Add(student);  
umlContext.SaveChanges();

After executing the Main program, on the database, for table StudentProfiles now is:

and for table Students:

One way to prevent this is using data annotations, but I don't like this approach due the domain classes needs additional code:

public class Student
{
    public int Id{ get;  set;} 
    public string Name{ get;  set;}
    [Required]
    public virtual StudentProfile StudentProfile { get; set; } 
}

Questions:

1. Is it a bug from the fluent API?
2. Is there any way to solve this problem using the Fluent API without modifying the domain classes?

Thanks in advance!