ComboBox tab completion fails under some scenarios

[tznind]

Describe the bug

Tab completion in ComboBox works the first time you type something in but fails when changing and Tab completing the second time.

To Reproduce
Using the below code

• Tab into the ComboBox
• Type "Le"
• Press Down to select "Left", it auto completes as expected
• Hit Tab (to move focus to Label)
• ComboBox completes to "Left" as expected
• Hit Tab (to refocus the ComboBox)
• Delete the text and type "Ri"
• Press Down to select "Right", it auto completes as expected
• Hit Tab
• See error

The expected behaviour is for the text to behave as before and leave "Right" selected in combo box

Actual behaviour is that it resets to "Left"

using System.Collections.ObjectModel;
using Terminal.Gui;

namespace delmev2
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Application.Init();


            var d = new Dialog()
            {
                Width = 50,
                Height = 10
            };

            var lbl = new Label()
            {
                Text = "Side:",
                Width = 10,

                // The thing we want
                CanFocus = true,
            };
            d.Add(lbl);

            var dropdown = new ComboBox()
            {
                X = Pos.Right(lbl),
                Width = 10,
                Height = 5
                
            };

            dropdown.SetSource(new ObservableCollection<Side>(Enum.GetValues(typeof(Side)).Cast<Side>()));
            d.Add(dropdown);

            Application.Run(d);
            Application.Shutdown();

        }
    }
}