DockXamlSample program does not show TextBoxes

[RPBeatty]

The DockXamlSample sample program has TextBlock/TextBox children in various docked panes of the MainView.axaml file.
However none of them are displayed when I run the program.
Am I missing something... or is there is a bug in this non-MVVM example?
The DockMvvmSample sample program seems to work.

[RPBeatty]

When I deleted "TryToUseIdAsKey="True"" from this line in App.axaml, then the TextBox/TextBlocks are shown.
I don't understand why however.

<ControlRecycling x:Key="ControlRecyclingKey" TryToUseIdAsKey="True"/>