To reproduce: add a RadBindingNavigator and a RadDataEntry

Use the following code:

RadDropDownList ddl;
BindingSource bs;

public Form1()
{
    InitializeComponent();

    this.radDataEntry1.EditorInitializing += radDataEntry1_EditorInitializing;
    bs = new BindingSource();

    DataTable dt = new DataTable();
    dt.Columns.Add("ID", typeof(int));
    dt.Columns.Add("Description", typeof(string));
    dt.Columns.Add("Code1", typeof(string));
    dt.Columns.Add("Code2", typeof(string));
           
    dt.Rows.Add(1, "Description", "DE", "CD");
    dt.Rows.Add(2, "Description", "CD", "AB");
    dt.Rows.Add(3, "Description", "BC", "DE");
    bs.DataSource = dt;  
    this.radDataEntry1.DataSource = this.radBindingNavigator1.BindingSource = bs;
}

private void radDataEntry1_EditorInitializing(object sender, Telerik.WinControls.UI.EditorInitializingEventArgs e)
{
    if (e.Property.Name == "Code1" || e.Property.Name == "Code2")
    {
        ddl = new RadDropDownList();
        using (ProvinceCodesEntities dbContext = new ProvinceCodesEntities())
        {
            IEnumerable<ProvinceCode> codeList = dbContext.ProvinceCodes.ToList();

            ddl.DataSource = codeList;
            ddl.DisplayMember = "ProvinceCode1";
            ddl.ValueMember = "ProvinceCode1";
        }
        e.Editor = ddl;
    }
}

When you run the application, you will notice that only the first item in the collection has incorrect mapped values for the properties which use RadDropDownList as an editor. When navigating to the next items, the values are OK.

Workaround:

RadDropDownList ddl;
BindingSource bs;

public Form1()
{
    InitializeComponent();
    this.radDataEntry1.EditorInitializing += radDataEntry1_EditorInitializing;
    bs = new BindingSource();

    DataTable dt = new DataTable();
    dt.Columns.Add("ID", typeof(int));
    dt.Columns.Add("Description", typeof(string));
    dt.Columns.Add("Code1", typeof(string));
    dt.Columns.Add("Code2", typeof(string));
           
    dt.Rows.Add(1, "Description", "DE", "CD");
    dt.Rows.Add(2, "Description", "CD", "AB");
    dt.Rows.Add(3, "Description", "BC", "DE");
    bs.DataSource = dt;  
}

private void radDataEntry1_EditorInitializing(object sender, Telerik.WinControls.UI.EditorInitializingEventArgs e)
{
    if (e.Property.Name == "Code1" || e.Property.Name == "Code2")
    {
        ddl = new RadDropDownList();
        using (ProvinceCodesEntities dbContext = new ProvinceCodesEntities())
        {
            IEnumerable<ProvinceCode> codeList = dbContext.ProvinceCodes.ToList();
            
            ddl.DataSource = codeList;
            ddl.DisplayMember = "ProvinceCode1";
            ddl.ValueMember = "ProvinceCode1";
            ddl.Parent = this;
        }
        e.Editor = ddl;
    }
}

private void Form1_Load(object sender, EventArgs e)
{
    this.radDataEntry1.DataSource = this.radBindingNavigator1.BindingSource = bs;
}