Can't clear the autocomplete textbox

Describe the bug

Trying to programmatically clear the autocomplete textbox using:
firstNameText.Text = string.Empty;
or
firstNameText.Text = ""
and also
firstNameText.PreviewTextInput -= firstNameText_Preview;
firstNameText.Text = string.Empty;
firstNameText.InvalidateVisual();
firstNameText.PreviewTextInput += firstNameText_Preview;

but the autocompletetextbox won't clear.

Steps to reproduce the bug

Create an autocompletetextbox
Bind that autocompletetextbox's itemsource to an observablecollection.
Create a button
Attach a function to that button that clears the autocompletetextbox.Text.

Pick a selection from the dropdown.
Press the button you created.

Expected behavior

I expected the text to clear.

Screenshots

No response

NuGet package version

HandyControl 3.4.0

IDE

Visual Studio 2019

Framework type

No response

Windows version

May 2021 Update (19043)

Additional context

No response

Start at the AutoCompleteTextBox implementation and reproduce the issue with an ItemsSource, a selected dropdown item, and a button that assigns an empty string to Text. Trace how the displayed value is updated after selection; done means clearing Text removes the visible text in that sequence.