AssemblyLoadContext unloading fails when custom usercontrol instance is created in plugin

[wwjwm]

Example is copied from https://github.com/dotnet/samples/tree/main/core/tutorials/Unloading.
The Host project and Plugin project in the example are recreated as WPF application and WPF library respectively.
The PluginClass class is modified as following and the unloading issue is as shown in the code snippet.

public class PluginClass : Interface
{
    //......

    public string GetMessage()
    {
        //new UserControl();               -------------->Uncomment this line, unloading success

        //new CustomUserControl();  --------------->Uncomment this line, unloading fails

        return "Hello from the unloadable plugin";
    }

    //......
}

public class CustomUserControl : UserControl
{
}

[vitek-karas]

See dotnet/wpf#1764 - this is basically a known problem with WPF.

Closing as the problem is in WPF, not in runtime.