[BUG] WPF - ViewModelViewHost and RoutedViewHost not displaying DefaultContent

[AliveDevil]

Describe the bug
ViewModelViewHost and RoutedViewHost do not display default content on WPF platform for not set ViewModel or not-performed initial navigation.

Steps To Reproduce
Add ViewModelViewHost or RoutedViewHost to Window, add default content, do not set anything else.

Expected behavior
I expect the default content to be shown for RoutedViewHost and ViewModelViewHost when no viewmodel is set or navigation has been performed.

Screenshots
Instead of the screenshot here is a minimal repro - both working, and not working.
rx-repro.zip

Environment

• OS: Windows
• Version: 14.1.1, basically 9.8.9
• Platform: WPF

Additional context
For ViewModelViewHost this broke from 9.8.1 to 9.8.9
In case of RoutedViewHost: This is broken since atleast release 8.0.0.

[github-actions]

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