Error when parsing XAML with a line in it

[JoshWobbles]

I get an error when trying to parse the XAML this creates when I have a line in the markup. Path, rectangle etc all seem fine, but as soon as I draw a line it throws the following error:

System.Xaml.XamlObjectWriterException
HResult=0x80131500
Message=Set property 'System.Windows.FrameworkElement.Margin' threw an exception.
Source=System.Xaml
StackTrace:
at MS.Internal.Xaml.Runtime.ClrObjectRuntime.SetValue(Object inst, XamlMember property, > Object value)
Inner Exception 1:
ArgumentException: 'Auto,Auto,0,0' is not a valid value for property 'Margin'.

For reference, the code I am using to parse the XAML is:

        var sb = new StringBuilder();
        using (var xmlWriter = new XamlXmlWriter(sb))
        {
            designSurface.SaveDesigner(xmlWriter);
        }
        var xamlCode = sb.ToString();

        UIElement rootElement;
        rootElement = (UIElement)XamlReader.Parse(xamlCode);