To reproduce use the code below and try to type in "000" in a cell

            GridViewComboBoxColumn comboColumn = new GridViewComboBoxColumn("Phone");
            radGridView1.Columns.Add(comboColumn);
            comboColumn.DataSource = new string[] { "0", "00", "000", "0001" };
            comboColumn.Width = 200;
            comboColumn.DropDownStyle = RadDropDownStyle.DropDown;
            comboColumn.AutoCompleteMode = AutoCompleteMode.Suggest;