Entity Framework Model First Database with inheritance strange bug

Question

I am learning EF and Model First approach. I had created a test app and all works, but with strange bug. I have a table, which has inheritance.

Here it is my EDM scheme: http://gyazo.com/fbec21b5fbfc47dd76ff3eaa38f86d36.png

Also i had a three rows in my Person and Employee tables. And this is how i select Data from the employee table:

private static void GetEmployees()
    {
        using (EmployeesModelContainer context = new EmployeesModelContainer())
        {
            int rowNumber = 0;

            var selectEmployeesQuery = from employee in context.Persons.OfType<Employee>()
                                       select employee;

            foreach (var employee in selectEmployeesQuery)
            {
                Console.WriteLine("{0}. {1} {2} ({3} лет, {4}, {5} образование) - {6}.", ++rowNumber, employee.Name, employee.Surname, employee.Age, (employee.Sex == Sex.Man) ? "Муж" : "Жен", employee.EducationLevel.Level, employee.Profession.NameOfProfession);
            }
        }
    }

And here it is what output i have: http://gyazo.com/f2b5f9f052f2a352b6d7ef01a20904f2.png You can see that after third row i have an empty row! I broke my head from where it is adding!

If i change my SelectQuery like this all will be allright.

var selectEmployeesQuery = from employee in context.Persons
                           select employee;

P/S. I am not sure about my other queries, INSERT, UPDATE and DELETE. Am i right?

private static void AddNewEmployee()
    {
        using (EmployeesModelContainer context = new EmployeesModelContainer())
        {
            Employee newEmployee = new Employee
            {
                Name = "Вася",
                Surname = "Пупкин",
                Age = 34,
                Sex = Sex.Man,
                ProfessionId = 4,
                EducationLevelId = 1
            };

            context.Persons.Add(newEmployee);

            context.SaveChanges();
        }
    }

    private static void UpdateEmployee()
    {
        using (EmployeesModelContainer context = new EmployeesModelContainer())
        {
            var updateEmployeeQuery = (from employee in context.Persons.OfType<Employee>()
                                       where employee.Name == "Вася"
                                       select employee).FirstOrDefault();

            updateEmployeeQuery.Age = 39;
            updateEmployeeQuery.EducationLevelId = 2;

            context.SaveChanges();
        }
    }

    private static void DeleteEmployee()
    {
        using (EmployeesModelContainer context = new EmployeesModelContainer())
        {
            var deleteEmployeeQuery = (from employee in context.Persons.OfType<Employee>()
                                       where employee.Name == "Вася"
                                       select employee).FirstOrDefault();

            context.Persons.Remove(deleteEmployeeQuery);

            context.SaveChanges();
        }
    }

The question is, If I need to add or delete some data in Employees table, why i am adding or deleting in Person table and it is allright? Data adding in Person and in Employees tables. And if I Updating some data in Employees table, why the data is updating in Person table correctly?