Why does context.SaveChanges() update every row in the table?

I wrote some code using C# and Entity Framework 6 (EF6) with MySql. The IDE is Visual Studio 2019 preview.

I installed these packages:

<packages>
  <package id="EntityFramework" version="6.2.0" targetFramework="net461" />
  <package id="MySql.Data" version="6.10.8" targetFramework="net461" />
  <package id="MySql.Data.Entity" version="6.10.8" targetFramework="net461" />
</packages>

Inserting and Selecting are works correctly but Updating works wired.

I put some number(something like 2 or 100) into tbx_CarId and I expected that EF6 updates only ONE row, but it updates every low in the table.

private void btn_update_Click(object sender, EventArgs e)
{
    using (MySqlConnection connection = new MySqlConnection(connectionString))
    {
        connection.Open();

        using (Parking context = new Parking(connection, false))
        {
            context.Database.Log = (string message) => { Console.WriteLine(message); };

            int targetId = Int32.Parse(tbx_CarId.Text);
            var blogs = from b in context.Cars
                        where b.CarId == targetId
                        select b;
            Car item = blogs.Single();
            item.Model = tbx_NewModel.Text;
            int numOfSavedLows = context.SaveChanges();
            Console.WriteLine("numOfSavedLows: " + numOfSavedLows.ToString());
        }
    }
}

The method context.SaveChanges() always returns an exact number, 1, and on the console window, "numOfSavedLows: 1" is printed.

But the every row is changed whenever I execute that method.

Also, the logger of EF6 writes on the console something like this:

Started transaction at 2019-01-03 오후 6:47:59 +09:00
`Car_Update`
-- CarId: '2' (Type = Int32, IsNullable = false)
-- Model: 'new value of the model' (Type = String, IsNullable = false, Size = 5)
-- Year: '2013' (Type = Int32, IsNullable = false)
-- Manufacturer: 'Dodge' (Type = String, IsNullable = false, Size = 5)
-- Executing at 2019-01-03 오후 6:47:59 +09:00
-- Completed in 6 ms with result: 16

Committed transaction at 2019-01-03 오후 6:47:59 +09:00
Disposed transaction at 2019-01-03 오후 6:47:59 +09:00

Please look at the line -- Completed in 6 ms with result: 16 The number(in this case, 16) is the count of every row in Car table.

Why does EF6 update every low? How can I fix it?

The rest of the codes are here:

[DbConfigurationType(typeof(MySqlEFConfiguration))]
class Parking : DbContext
{
    public DbSet<Car> Cars { get; set; }

    public Parking()
      : base()
    {
        // constructor is empty
    }

    // Constructor to use on a DbConnection that is already opened
    public Parking(DbConnection existingConnection, bool contextOwnsConnection)
      : base(existingConnection, contextOwnsConnection)
    {
        // constructor is empty
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<Car>().MapToStoredProcedures();
    }
}

and

class Car
{
    public int CarId { get; set; }
    public string Model { get; set; }
    public int Year { get; set; }
    public string Manufacturer { get; set; }
}

Most of the codes are from here: https://dev.mysql.com/doc/connectors/en/connector-net-entityframework60.html

update 1: The table Cars looks like this (The schema and table are generated by EF6 automatically)

update 2: The values of the rows are like this: Before and After (args are 8, 'new value')