c# - Comboboxes are linked for some reason

Question

I have the following code to populate 3 comboboxes:

private void PopulateDDLs()
{
    SqlConnection connection;
    SqlCommand command;
    SqlDataReader reader;
    DataTable dt;

    using (connection = new SqlConnection("connection string here"))
    {
        using (command = new SqlCommand("sql query here", connection))
        {
            connection.Open();
            using (reader = command.ExecuteReader())
            {
                dt = new DataTable();
                dt.Load(reader);

                ddl1.ValueMember = "col1";
                ddl1.DisplayMember = "col2";
                ddl1.DataSource = dt;

                ddl2.ValueMember = "col1";
                ddl2.DisplayMember = "col2";
                ddl2.DataSource = dt;

                ddl3.ValueMember = "col1";
                ddl3.DisplayMember = "col2";
                ddl3.DataSource = dt;
            }
            connection.Close();
        }
    }
}

However, when I execute this program, and make a selection from one of the comboboxes, the same value automatically gets selected from the other comboboxes. Any idea why this is happening and how to stop it from happening more importantly?

If I create 3 functions, 1 for each combobox, then everything works fine.

This project is a Word Document level project for Word 2010 created using .NET-4.0 using VS2013.

Answer 1

New much improved solution:

A DataSource is more than just the data.

There is hidden default BindingSource that makes the ComboBoxes follow.

To avoid this coupling and also the data replication in the first version of this answer, all you need to do is create a separate BindingSource for each ComboBox. These share the DataTable but have each its own rowPointer:

BindingSource bS1, bS2, bS3;
..
..    
..
..    
dt = new DataTable();
dt.Load(reader);

bS1 = new BindingSource();
bS1.DataSource = dt; 
bS2 = new BindingSource();
bS2.DataSource = dt; 
bS3 = new BindingSource();
bS3.DataSource = dt;
..
ddl1.DataSource = bS1 ;
ddl2.DataSource = bS2 ;
ddl3.DataSource = bS3 ;
..
..

Now the ComboBoxes can be changed independently.

Note: My first version worked but was the wrong way do it. Sorry..!