EntityFramework - DisconnectedEntity

Course c = new Course();

using (var db = new ContosoUniversityEntities())
{
    c = db.Course.Find(2);
    Console.WriteLine(db.Entry(c).State); // Unchange

    c.Title += ".";
    Console.WriteLine(db.Entry(c).State); // Midified
}

using (var db = new ContosoUniversityEntities())
{
    Console.WriteLine(db.Entry(c).State); // Detached

    db.Course.Attach(c);
    Console.WriteLine(db.Entry(c).State); // Unchange

    db.Entry(c).State = EntityState.Modified;
    Console.WriteLine(db.Entry(c).State); // Midified

    db.SaveChanges();
}