Theme changes don't work correctly after opening the About box

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### Windows Terminal version

1.12.3472.0

### Windows build number

10.0.19041.1415

### Other Software

_No response_

### Steps to reproduce

1. Start Windows Terminal (don't just use an existing session).
2. Open the Settings UI, and go to the _Appearance_ section.
3. Set the _Theme_ to _Light_, and click _Save_.
4. Without closing the settings, open the _About_ box, and close it again.
5. Now switch the _Theme_ to _Dark_, and click _Save_.

### Expected Behavior

The UI colors should change to the dark theme.

### Actual Behavior

Most of the UI remains using the light theme, but some elements appear to be updated in such a way that they become invisible.


This breaks in a similar way when switching from dark to light, and it's also not only the _About_ box that triggers it - I think any popup dialog will do (e.g. the "Do you want to close all tabs?" warning has the same effect).

If you open the _About_ box again, it temporarily "fixes" the problem (i.e. it refreshes the colors correctly), but that only last until you try and change the theme again.

Reproduce the issue in Windows Terminal using the Settings UI's Appearance section, then compare theme updates after closing the About box or another popup dialog. Done means switching between light and dark updates all UI colors correctly without invisible elements.

Written by the indexing model from the issue text.