Telerik: radpropertygrid does not seem to render nested classes in collection editor/picker

See more:

XAML

WPF

C#5.0

Telerik

My problem is that Collections on second level do not render members of inner (nested) classes.

Second level means inside Collections Add/Remove editor (CollectionEditorPicker).

I'd expect that in the figure 2. would be shown all inner members of the class 'powerVoltageDefinition', just like we see it in the figure 1.

What is the trick ? How can I display such inner classes in this default Collection Add/Remove Editor (the so called 'CollectionEditorPicker')?

Figure 1 - Correctly rendered nested class members
https://i.stack.imgur.com/dWgo1.jpg

Figure 2 - Not rendered nested class members
https://i.stack.imgur.com/vwf3v.jpg

XAML snippet of this RadPropertyGrid:

<telerik:RadPropertyGrid x:Name="SelectedProperty" 

    AutoGenerateBindingPaths="True"
    AutoGeneratePropertyDefinitions ="True" 
    AutoGeneratingPropertyDefinition="RadPropertyGrid_AutoGeneratingPropertyDefinition"
    CanUserResizeDescriptionPanel="True"
    NestedPropertiesVisibility="Visible"
    DescriptionPanelVisibility="Visible"
        SearchInNestedProperties="True"                                                                                                      
        PropertySetMode="Union"                                                                                                  
        RenderMode="Hierarchical"
        EditMode="Default"
        EditEnded="CellEditEnded"
        ToolTip="ToDo: Tool Tips">

</telerik:RadPropertyGrid>

What I have tried:

I have already investigated:

1. This does not describe problem:
wpf - Telerik RadPropertyGrid Content of CollectionEditorPicker - Stack Overflow[^]

2. And this solution does not cover my nested class powerVoltageDefinition:
Access to CollectionEditorPicker inner property grid - PropertyGrid - UI for WPF Forum[^]

Does my solution lead to any of these ?:

1.
PropertyGridIndentPresenter Class[^]

2.
PropertyGridIndentPresenter.IndentLevelProperty Field[^]