WPF: GroupBox.SetResourceReference suddenly makes it inherit TemplateParent.Foreground

Question

I was making a UserControl when I found this strange phenomena. If I use C# code to place a GroupBox in the UserControl's template and then make any SetResourceReference call on the GroupBox, suddenly the GroupBox inherits the foreground of TemplateParent (my UserControl).

So far I have found the following requirements for this situation:

• UserControl base type does not matter
• Affected template child must be a GroupBox (but not necessarily the first template child)
• The foreground of the GroupBox may be explicitly set in the template, overriding the inherit
• Must be using some sort of reference call from the GroupBox
• Only the Foreground property seems to be affected

Here is my sample code:

MainWindow.xaml:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:my="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="350">
    <Window.Resources>
        <Thickness x:Key="TestPadding">5</Thickness>
        <Style TargetType="{x:Type GroupBox}">
            <Setter Property="Foreground" Value="Red" />
            <Setter Property="Background" Value="Orange" />
        </Style>
    </Window.Resources>
    <Grid>
        <my:TestControl Foreground="Blue" Background="Purple" />
    </Grid>
</Window>

TestControl.cs:

using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
using System.Windows.Media.Effects;
using System.Windows.Markup;

namespace WpfApplication1
{
    public class TestControl : UserControl
    {
        public TestControl()
        {
            FrameworkElementFactory group = new FrameworkElementFactory(typeof(GroupBox));
            group.SetValue(GroupBox.ContentProperty, "My Child");
            group.SetResourceReference(GroupBox.MarginProperty, "TestPadding");
            this.SetValue(TestControl.TemplateProperty, new ControlTemplate(typeof(TestControl)) { VisualTree = group });
        }
    }
}

What do you guys think, is this a bug that I should report to Microsoft?

Answer 1

I have contacted the Microsoft WPF Development Team. They acknowledge this as a bug, but have prioritised it as low and not likely to be fixed.

My work around for this example: Use another control to take the *.SetResourceReference call to perform padding, instead of the GroupBox.