ComboBox Autocomplete: works wrong

I have an application when user can type the text. There is a combobox on a toolbar that allows user to change the selected font of the text to another. The autocomplete doesn't work when user selects whole text in combobox and start typing.

Part of code:

    ComboBox aComboBox = new ComboBox();
    aComboBox.DropDownStyle = ComboBoxStyle.DropDown;
    aComboBox.AutoCompleteMode = AutoCompleteMode.Append;
    aComboBox.AutoCompleteSource = AutoCompleteSource.ListItems;
    aComboBox.Items.AddRange( new object[] {"Segoe UI",  "Raavi", "Agency FB"} );

    aComboBox.SelectedIndex = 0;

    ToolStripItem anItem = new ToolStripControlHost( aComboBox );
   aTextEditToolstrip.Items.Add( anItem );

Steps to reproduce:

1. Type in combobox first symbol e.g. 'r'

3. The autocomplete suggests 'Raavi' font

4. Select whole word

5. Type symbol 'r' again

Nothing is happened, autocomplete doesn't suggest any variants.

Please, help to resolve this problem.