[cairo] Horizontal artifacts rendering to an image surface

[Floyd May]

I've been able to boil this down to a reproducible, small case.
Basically, two four-point polygons where one edge from each is
collinear.  Using even-odd rendering, I'm getting these artifacts:

http://imagebin.org/222354

Again, this is based on v 1.10.2, on Windows (both x86 and x64 exhibit
the issue), based on a recent download of GTK+ binaries.

Here is C# source (using Mono.Cairo; should be able to adapt to C code
relatively easily):

    class Program
    {
        static void Main(string[] args)
        {
            var records = new Cairo.PointD[][]{
                new Cairo.PointD[]{
                    new Cairo.PointD(448.948314981535,
264.938083162531),
                    new Cairo.PointD(448.51546072308, 220.797386273742),
                    new Cairo.PointD(530, 220),
                    new Cairo.PointD(561.332719124854,
261.581040261313),
                },
                new Cairo.PointD[]{
                    new Cairo.PointD(339.794010419399,
236.296868257225),
                    new Cairo.PointD(346.503195904195,
229.764422696084),
                    new Cairo.PointD(448.474225856364,
216.590856667608),
                    new Cairo.PointD(448.948314981535, 264.938083162531)
                },
            };
            
            using (var surface = new
Cairo.ImageSurface(Cairo.Format.Argb32, 1024, 1024))
            {
                using (var ctx = new Cairo.Context(surface))
                {
                    ctx.FillRule = Cairo.FillRule.EvenOdd;

                    foreach (var ring in records)
                    {
                        ctx.MoveTo(ring.First());

                        foreach (var pt in ring.Skip(1))
                        {
                            ctx.LineTo(pt);
                        }

                        ctx.ClosePath();
                    }

                    ctx.SetSourceColor(0, 0.5, 1);
                    ctx.FillPreserve();
                    ctx.SetSourceColor(0, 0, 0);
                    ctx.Stroke();
                }

                surface.Flush();

                surface.WriteToPng("image.png");
            }
        }
    }