Rhino GUI do not show WPF Expander.Header content when it is not only text

Rhino Developer
1

When changing code from:

<Expander Header="Demand Points"/>

to

 <Expander>
    <Expander.Header>
        <StackPanel Orientation="Horizontal" >
            <TextBlock  Text="Demand Points"/>
            ...
        </StackPanel>
    </Expander.Header>
</Expander>

then Rhino do not display Exapnder header any more. It work with normal WPF application.

2

TextBlock: what style is associated?
Could the font size be zero?
Could the font color be the same as the background?
Could the size of the StackPanel zero? (use a Border with a color to check this)

Never trust the Visual Studio designer, it usually shows different results compared to runtime.

3

I used same code in WPF Application and that behaved correctly in runtime.

Even following code do not work. (That is only WPF / XAML code in project. There can not be any external referencing )

<UserControl x:Class="CFL.Panes.HDBPane"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d" Width="496" Height="485">

     <Grid>
        <Expander>
            <Expander.Header>
                <Label>Something</Label>
            </Expander.Header>
        </Expander>
    </Grid>
    
</UserControl>