CommandBinding broken in inner Custom Control when nesting two Custom Controls of the same type.

Question

I've done a Custom Control in form of a GroupBox but with an extra header which purpose is to hold a button or a stackpanel with buttons at the other side.

I've added the a Dependency Property to hold the extra header and I've connected the customized template.

Everything works fine until I put one of these controls in another one. Now the wierd stuff begins(at least in my eyes xP), the command binding in the inner control simply isn't set. I tried to use Snoop to gather some data, the see if the inherits is broken and when I clicked on the buttons which isn't doing what I want it to, boom, breakpoint triggered.

So in some wierd way the Command isn't set until something that I don't know what it is, happens, which snoops triggers.

I've also tried to put the buttons in the regular Header property and that works fine, but not with my own made. I could just switch places with them to make it like I want but now I'm curious to know where the problem lies...

Now I wonder, what can I've missed?

The control class:

public class TwoHeaderedGroupBox : GroupBox
{
    static TwoHeaderedGroupBox()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(TwoHeaderedGroupBox), new FrameworkPropertyMetadata(typeof(TwoHeaderedGroupBox)));
    }

    public static DependencyProperty HeaderTwoProperty = DependencyProperty.Register("HeaderTwo", typeof(object), typeof(TwoHeaderedGroupBox), new FrameworkPropertyMetadata());     

    public object HeaderTwo
    {
        get { return (object)GetValue(HeaderTwoProperty); }
        set { SetValue(HeaderTwoProperty, value);}
    }      
}

And here is the Template (which by the way is created by blend from the beginning):

<ControlTemplate TargetType="{x:Type Controls:TwoHeaderedGroupBox}">
    <Grid SnapsToDevicePixels="true">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="6"/>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="6"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="6"/>
        </Grid.RowDefinitions>
        <Border BorderBrush="Transparent" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.ColumnSpan="4" Grid.Column="0" CornerRadius="4" Grid.Row="1" Grid.RowSpan="3"/>
        <Border x:Name="Header" Grid.Column="1" Padding="3,1,3,0" Grid.Row="0" Grid.RowSpan="2" VerticalAlignment="Center">
            <ContentControl Content="{TemplateBinding Header}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
        </Border>   
        <ContentPresenter Grid.ColumnSpan="2" Grid.Column="1" Margin="{TemplateBinding Padding}" Grid.Row="2" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
        <Border BorderBrush="White" BorderThickness="{TemplateBinding BorderThickness}" Grid.ColumnSpan="4" CornerRadius="4" Grid.Row="1" Grid.RowSpan="3">
            <Border.OpacityMask>
                <MultiBinding ConverterParameter="7" Converter="{StaticResource BorderGapMaskConverter}">
                    <Binding ElementName="Header" Path="ActualWidth"/>
                    <Binding Path="ActualWidth" RelativeSource="{RelativeSource Self}"/>
                    <Binding Path="ActualHeight" RelativeSource="{RelativeSource Self}"/>
                </MultiBinding>
            </Border.OpacityMask>
            <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="3">
                <Border BorderBrush="White" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="2"/>
            </Border>
        </Border>
        <Border x:Name="HeaderTwo" Grid.Column="2" Padding="3,5,3,5" Grid.Row="0" Grid.RowSpan="2" HorizontalAlignment="Right">
            <ContentControl Content="{TemplateBinding HeaderTwo}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" DataContext="{TemplateBinding DataContext}"/>
        </Border>
    </Grid>
</ControlTemplate>