Bug: Same context menus goes out of sync.

Reproduction: 
    
    Create window, with xaml:
    <Grid>
        <Grid.ContextMenu>
            <ContextMenu x:Name="contextMenuMain">
                <MenuItem Header="Blaa" />
            </ContextMenu>
        </Grid.ContextMenu>
        
        <Hardcodet:TaskbarIcon 
            x:Name="MainTaskbarIcon"
            ContextMenu="{Binding ElementName=contextMenuMain}"
        />
    </Grid>
    
    1.) Start the program, right click on taskbar icon to open contextmenu.
    2.) In program grid, right click to open contextmenu. (*This jumps to bottom of the screen*)
    
    Edit: Steps as image http://users.jyu.fi/~jaotospe/2.before-after.jpg
    
Patch fix:    
TaskbarIcon.cs:
http://users.jyu.fi/~jaotospe/wpf_trayicon_patch_wrongly_placed_contextmenu.txt