To repeoduce: - Set the AutoCompleteMode to suggest and paste some text in the drop down list. Workaround: protected override void OnLoad(EventArgs e) { base.OnLoad(e); radDropDownList1.TextChanged += radDropDownList1_TextChanged; } void radDropDownList1_TextChanged(object sender, EventArgs e) { this.radDropDownList1.DropDownListElement.AutoCompleteSuggest.HandleAutoSuggest(this.radDropDownList1.Text); }