Programmatic adding items to radCheckedDropDownList throws error

Hi all

I'm working with Visual Studio 2017, .NET 4.6.1, Telerik UI for WinForms 2018.2.621

This is the code:

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using Telerik.WinControls.UI;

namespace TelerikTest
{
    public partial class Form1 : Form
    {
        private List<string> list = new List<string>() { "one", "two", "three" };
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            radCheckedDropDownList1.Items.Clear();

            foreach (string item in list)
            {
                radCheckedDropDownList1.Items.Add(new RadCheckedListDataItem(item, false));
            }
        }
    }
}

If I fill the radCheckedDropDownList after having selected an item by click (SelectByClick.png) all is fine.

If I fill the radCheckedDropDownList after having selected an item using autocomplete (SelectByAutoComplete.png), I get a NullReferenceException (NullReferenceException.png).

Could someone please tell me, what I'm doing wrong?

Thanks in advance

Daniel