ContentDialog does not follow RequestedTheme properly in XAML Islands

[aquinn39]

Describe the bug

When a ContentDialog is shown within an XAML Island and it's RequestedTheme does not match the current Windows theme, it does not apply properly (See screenshot below) - mainly the buttons appear to use the wrong RequestedTheme.

Steps to reproduce the bug

1. Create an app that uses WinUI 2 with XAML Islands (Tutorial here: https://docs.microsoft.com/en-us/windows/apps/desktop/modernize/host-standard-control-with-xaml-islands).
2. Set Windows' app mode to Dark
3. Create a ContentDialog with it's requested theme set to Light in XAML and show it.

Expected behavior

The buttons should be in light mode, like the rest of the dialog. This is what happens with the same setup in a UWP app:

Screenshots

Here is a ContentDialog in an XAML Island with its RequestedTheme set to Light while the Windows theme is set to dark. Notice that the buttons don't seem to realise they should be in light mode, making the text very hard to read:

NuGet package version

Microsoft.UI.Xaml 2.8.0

Windows app type

• [ ] UWP
• [ ] Win32

Device form factor

Desktop

Windows version

Windows 11 (21H2): Build 22000

Additional context

No response