The control is misplaced when you zoom in/out the browser window.

To work this around you can manually calculate and set the top and left positions of the HTML presenter. 

this.htmlPlaceholder.Loaded += (sender, args) => { this.htmlPlaceholder.LayoutUpdated += htmlPlaceholder_LayoutUpdated; };

private void htmlPlaceholder_LayoutUpdated(object sender, EventArgs e)
{
    this.Dispatcher.BeginInvoke(delegate
    {
        double controlTop = GetTop();
        double controlLeft = GetLeft();
 
        htmlPlaceholder.HtmlPresenter.SetStyleAttribute("top", controlTop + "px");
        htmlPlaceholder.HtmlPresenter.SetStyleAttribute("left", controlLeft + "px");
    });           
}