Namespace Problem for NavigationView in VB？

[MyBlueHorizon]

I use this code look like right but I get Error. (Some code has been omitted)

In MainWindow.xmal
<ui:FluentWindow x:Class="MainWindow"
    xmlns:local="clr-namespace:ProjectTest"
    xmlns:pages="clr-namespace:**ProjectTest.Pages**"
    <ui:NavigationViewItem
        TargetPageType="{x:Type pages:HomePage}">
    </ui:NavigationViewItem>
</ui:FluentWindow>

In HomePage.xmal
<Page x:Class="ProjectTest.Pages.HomePage"
      xmlns:local="clr-namespace:**ProjectTest.Pages**"
</Page>

In HomePage.xmal.vb
Namespace **Pages**
    Partial Public Class HomePage
    End Class
End Namespace

I get

System.InvalidCastException:“PageType of the $Wpf.Ui.Controls.INavigationViewItem must be derived from System.Windows.FrameworkElement. ProjectTest.Pages.HomePage is not.”

However, I change code to something looks like wrong, it work. (Some code has been omitted)

In MainWindow.xmal
<ui:FluentWindow x:Class="MainWindow"
    xmlns:local="clr-namespace:ProjectTest"
    xmlns:pages="clr-namespace:**ProjectTest.ProjectTest**.Pages"
    <ui:NavigationViewItem
        TargetPageType="{x:Type pages:HomePage}">
    </ui:NavigationViewItem>
</ui:FluentWindow>

In HomePage.xmal
<Page x:Class="ProjectTest.Pages.HomePage"
      xmlns:local="clr-namespace:**ProjectTest.ProjectTest**.Pages"
</Page>

In HomePage.xmal.vb
Namespace **ProjectTest.Pages**
    Partial Public Class HomePage
    End Class
End Namespace

I‘m not sure it is a bug or it really should be this。