Incorrectly difference operation on BREPs

Question

I make a CAD program using eyeshot (2022/2023). From the very beginning I've been facing problems with Boolean operations, in this case the difference operation. To illustrate my problem I prepared a demo in which this problem occurs.

From the red I-Beam figure, I want to cut a blue figure.

After the difference operation I get this result.

As you can see, I get strange walls in a place where they shouldn't be.

protected override void OnContentRendered(EventArgs e)
{
    design1.ActiveViewport.Grid.AutoSize = true;
    design1.ActiveViewport.Grid.Step = 100;
    design1.Layers[0].Color = System.Drawing.Color.FromArgb(127, 127, 127);

//Creating I-Beam Brep
    Brep bar = IBeam(590, 300, 13, 25, 27, 500);
    //design1.Entities.Add(bar, design1.Layers[0].Name, System.Drawing.Color.Crimson);

//Creating box Brep
    Brep box = DrawBox();
    box.Translate(0, -1, 0.5);
    //design1.Entities.Add(box, design1.Layers[0].Name, System.Drawing.Color.Blue);

//Creating difference
    Brep[] diffArray = Brep.Difference(bar, box);

    if (diffArray != null)
    {
        Brep diff = diffArray.FirstOrDefault();
        design1.Entities.Add(diff);
    }

    design1.ZoomFit();
    design1.Invalidate();
    base.OnContentRendered(e);
}

private Brep DrawBox()
{
double height = 142;
double width = 144;
Point3D p1 = new Point3D(0, 0, 0);
Point3D p2 = new Point3D(0, 0, -height);
Point3D p3 = new Point3D(width, 0, -height);
Point3D p4 = new Point3D(width, 0, 0);

    List<ICurve> curves = new List<ICurve>() { new Line(p1, p2), new Line(p2, p3), new Line(p3, p4), new Line(p4, p1) };
    
    CompositeCurve curve = new CompositeCurve(curves, false);
    devDept.Eyeshot.Entities.Region reg = new devDept.Eyeshot.Entities.Region(curve, devDept.Geometry.Plane.XZ, true);
    Brep brep = reg.ExtrudeAsBrep(-26);
    return brep;
}

private static Brep IBeam(double w, double t, double h, double r, double j, double extrudeLength = 500.0)
{
CompositeCurve curve = IBeamStraightSketch(w, t, h, r, j);

    devDept.Eyeshot.Entities.Region reg = new devDept.Eyeshot.Entities.Region(curve, devDept.Geometry.Plane.YZ, true);
    Brep brepBeam = reg.ExtrudeAsBrep(extrudeLength);
    brepBeam.Rotate(Utility.DegToRad(90.0), Vector3D.AxisX, Point3D.Origin);
    brepBeam.Translate(0, 0, -t);
    return brepBeam;
}

public static CompositeCurve IBeamStraightSketch(double w, double h, double t, double p, double r)
{
double moveY = (h - t) / 2;
if (r \< 1) r = t;

    Point3D p1 = new Point3D(0, h);
    Point3D p2 = new Point3D(p, h);
    Point3D p3 = new Point3D(p, h - moveY + r);
    Point3D p4ArcTopLeftCenter = new Point3D(p + r, h - moveY + r);
    Point3D p7ArcTopRightCenter = new Point3D(w - p - r, h - moveY + r);
    Point3D p8 = new Point3D(w - p, h - moveY + r);
    Point3D p9 = new Point3D(w - p, h);
    Point3D p10 = new Point3D(w, h);
    Point3D p11 = new Point3D(w, 0);
    Point3D p12 = new Point3D(w - p, 0);
    Point3D p13 = new Point3D(w - p, moveY - r);
    Point3D p14ArcBottomRightCenter = new Point3D(w - p - r, moveY - r);
    Point3D p17ArcBottomLeftCenter = new Point3D(p + r, moveY - r);
    Point3D p18 = new Point3D(p, moveY - r);
    Point3D p19 = new Point3D(p, 0);
    Point3D p20 = new Point3D(0, 0);
    
    Line line1Left = new Line(p3, p2);
    Line line2Left = new Line(p2, p1);
    Line line3Left = new Line(p1, p20);
    Line line4Left = new Line(p20, p19);
    Line line5Left = new Line(p19, p18);
    
    Line line1Right = new Line(p8, p9);
    Line line2Right = new Line(p9, p10);
    Line line3Right = new Line(p10, p11);
    Line line4Right = new Line(p11, p12);
    Line line5Right = new Line(p12, p13);
    
    Arc aTopLeftIn = new Arc(p4ArcTopLeftCenter, r, Utility.DegToRad(-180), Utility.DegToRad(-90));
    Arc aTopRightIn = new Arc(p7ArcTopRightCenter, r, Utility.DegToRad(-90), Utility.DegToRad(0));
    Arc aBottomRightIn = new Arc(p14ArcBottomRightCenter, r, Utility.DegToRad(0), Utility.DegToRad(90));
    Arc aBottomLeftIn = new Arc(p17ArcBottomLeftCenter, r, Utility.DegToRad(90), Utility.DegToRad(180));
    
    Line lMiddleTop = new Line(aTopLeftIn.EndPoint, aTopRightIn.StartPoint);
    Line lMiddleBottom = new Line(aBottomRightIn.EndPoint, aBottomLeftIn.StartPoint);
    
    List<ICurve> lstElements = new List<ICurve>()
    {
        aTopLeftIn,
        lMiddleTop,
        aTopRightIn,
        line1Right,
        line2Right,
        line3Right,
        line4Right,
        line5Right,
        aBottomRightIn,
        lMiddleBottom,
        aBottomLeftIn,
        line1Left,
        line2Left,
        line3Left,
        line4Left,
        line5Left
    };
    CompositeCurve ccIBeam = new CompositeCurve(lstElements);
    
    ccIBeam.Rotate(Utility.DegToRad(90.0), Vector3D.AxisY, Point3D.Origin);
    
    return ccIBeam;

}

When I move the box figure in the Y-axis by 0.01 everything cuts out correctly and looks like below.

Unfortunately, this is not the solution to my problem. I can't move the components around until they finally graciously agree to cut correctly. I guess that the problem is that one of the I-Beam planes and one of the box planes lie in the same place. When I do a much simpler example of cutting two boxes between them, even if their walls lie in the same places such a problem does not occur there.

I feel that I've tried everything I can. I've tried using brep methods such as Regen(), Rebuild(), FixTopology(), UpdateBoundingBox(). They didn't work for my problem. The only solution I have been able to work out is to use on box scaling by 0.001 box.Scale(1.001, 1.001, 1.001); However, I feel that this is not a comprehensive solution to this problem and sooner or later I will run into more cases where the problem will recur.