Cannot enter a custom value in editable ComboBox

[jbrianceau]

Describe the bug

When using a ComboBox control having it's IsEditable property set to True and a predefined list of items, it is not possible for the user to enter a custom value which is a prefix of one of the items available in the list.

For instance, with:

<ComboBox IsEditable="True">
    <ComboBoxItem>12</ComboBoxItem>
    <ComboBoxItem>34</ComboBoxItem>
    <ComboBoxItem>56</ComboBoxItem>
    <ComboBoxItem>78</ComboBoxItem>
    <ComboBoxItem>79</ComboBoxItem>
</ComboBox>

It's possible for the user to set the ComboBox value to 2, 4, 6 but not possible to set it to 1, 3, 5, 7

Same issue with letters:

<ComboBox IsEditable="True">
    <ComboBoxItem>ab</ComboBoxItem>
    <ComboBoxItem>cd</ComboBoxItem>
    <ComboBoxItem>ef</ComboBoxItem>
    <ComboBoxItem>gh</ComboBoxItem>
    <ComboBoxItem>gi</ComboBoxItem>
</ComboBox>

It's possible for the user to set the ComboBox value to b, d, f but not possible to set it to a, c, e, g

Steps to reproduce the bug

1. Create a WinUI 3 project
2. Add the following snippet to MainWindow.xaml

<ComboBox IsEditable="True">
    <ComboBoxItem>12</ComboBoxItem>
    <ComboBoxItem>34</ComboBoxItem>
    <ComboBoxItem>56</ComboBoxItem>
    <ComboBoxItem>78</ComboBoxItem>
    <ComboBoxItem>79</ComboBoxItem>
</ComboBox>

3. Run the project
4. Try to set the ComboBox value to 1 for instance
5. Navigate away from the ComboBox

Note: it's also possible to get a repro with "WinUI 2 Gallery" and "WinUI 3 Gallery" apps

Expected behavior

I would expect that the ComboBox keeps the value entered by the user (1) and does not change it to 12 automatically.

Screenshots

• Custom project
  

• WinUI 3 Gallery
  

NuGet package version

Windows App SDK 1.2.4: 1.2.230217.4

Packaging type

No response

Windows version

Windows 11 version 22H2 (22621, 2022 Update), Windows 10 version 22H2 (19045, 2022 Update)

IDE

Visual Studio 2022

Additional context

No response

[ekdahl]

Still the same behavior with Windows App SDK 1.5.240227000