Memory leak with XAML and WindowsFormsHost

See more:

.NET3.5

.NET

XAML

forms

First I show you what I have and than I explain my problem.
I have a code where I can switch between styles depending on the property "Layout", which can be "Layout1" or "Layout2".

<Grid>
    <ContentControl Style="{Binding Layout}">
    </ContentControl>
</Grid>

Here are the Style definitions:

 <Style x:Key="Layout1" TargetType="{x:Type ContentControl}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ContentControl}">
                .....
                <ContentControl Style="{StaticResource myWindow}">
                </ContentControl>
                .....
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

 <Style x:Key="Layout2" TargetType="{x:Type ContentControl}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ContentControl}">
                .....
                <ContentControl Style="{StaticResource myWindow}">
                </ContentControl>
                .....
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Each Style use the static ressource "myWindow". In myWindow is a class myControl and myControl use a WindowsFormsControl myControl5.

<Style x:Key="myWindow" TargetType="{x:Type ContentControl}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ContentControl}">
                <Grid >
                    <local:myControl Margin="0,0,0,0"
                    </local:myControl>
                </Grid>
             </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<Style TargetType="{x:Type local:myControl}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:myControl}">
                <WindowsFormsHost x:Name="PART_WindowsFormsHost">
                    <cbh:myControl5></cbh:myControl5>
                </WindowsFormsHost>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

In the class myControl I get the handle to myControl5 so I can use it to adding event handler.

public class myControl : Control
{
    public override void OnApplyTemplate ()
    {
        base.OnApplyTemplate ();
        this.windowsFormsHost = GetTemplateChild ("PART_WindowsFormsHost") as WindowsFormsHost;
        myControl5 mc5 = this.InnerControl;
        mc5.GotFocus += new EventHandler(InnerControl_GotFocus);
        .....
    }
}

Now my problem:
Each time the Style Layout change, I see that WPF creates a new myControl but never release it. So the memory usage increase each time.
I hope the explaining is so useful, that you can say "Natch, you forgot ..." or something like that.