GDI+, Somethimes Control is drawing with different Pen, Help

  // based on BitLineControl
    public partial class LineControl : ShapeControl
    {
      
        private Point StartPoint;
        private Point EndPoint;
        
        private Point[] _points = new Point[4];
        
        public LineControl(int x1,int y1, int x2, int y2, int zoom):base (x1,y1,x2-x1,y2-y1,zoom)
        {
            this.StartPoint = new Point(x1, y1);
            this.EndPoint = new Point(x2, y2);
            col = Color;
            thick = Thickness;
            double currZoom = Utility.zoomFactor[zoom];
            this.origanalValues = new int[] { (int)(x1 / currZoom), (int)(y1 / currZoom), (int)(x2 / currZoom), (int)(y2 / currZoom), (int)(thick / currZoom) };          
            p = new Pen(col, thick);
            p.DashStyle = DashStyle.Solid;

            b = new SolidBrush(col);
            drawLine(StartPoint, EndPoint);
            String s = this.Equation;
            
            InitializeComponent();
        }
        public void updateThickness (int thickness){
            this.thick = thickness;
            this.drawLine(this.StartPoint, this.EndPoint);
        }
        private void drawLine(Point firstpoint, Point secondpoint)
        {
            
            this.SetStyle(ControlStyles.DoubleBuffer |
                 ControlStyles.AllPaintingInWmPaint |
                 ControlStyles.ResizeRedraw |
                 ControlStyles.UserPaint |
                 ControlStyles.SupportsTransparentBackColor, true);
            this.UpdateStyles();
            path= new GraphicsPath();

            _points[0] = firstpoint;
            _points[1] = secondpoint;
            double c = Math.Sqrt(Math.Pow((secondpoint.Y - firstpoint.Y),2) + Math.Pow((secondpoint.X - firstpoint.X),2));
            double cos = Math.Abs(secondpoint.Y - firstpoint.Y) / c;
            double sin = Math.Abs(secondpoint.X - firstpoint.X) / c;
            int b = (int)(sin * thick);
            int a = (int)(cos * thick);
            _points[2] = new Point(secondpoint.X + a, secondpoint.Y + b);
            _points[3] = new Point(firstpoint.X + a, firstpoint.Y + b);

            _points = setInitialPoints(_points);
            path.StartFigure();
            path.AddPolygon(_points);
            path.CloseFigure();
            base.Width += 2;
        }
        // updates Base.Top, Base.Left to determine size of control
        private Point[] setInitialPoints(Point[] oldPoints)
        {
            int theXvalue = 0;
            int theYvalue = 0;
            int maxX = 0;
            int maxY = 0;

            GraphicsPath gp = new GraphicsPath();
            Point[] newPoint = new Point[oldPoints.Length];
            Point oldValue = new Point();


            foreach (Point p in oldPoints)
            {
                if (oldValue.IsEmpty) { theXvalue = p.X; theYvalue = p.Y; maxX = p.X; maxY = p.Y; }
                else
                {
                    if (theXvalue > p.X) theXvalue = p.X;
                    if (theYvalue > p.Y) theYvalue = p.Y;

                    if (maxX < p.X) maxX = p.X;
                    if (maxY < p.Y) maxY = p.Y;
                }
                oldValue = p;
            }

            base.Left = (int)theXvalue;
            base.Top = (int)theYvalue;
            base.Width = (int)(maxX - theXvalue);
            base.Height = (int)(maxY - theYvalue);
            //base.Width += 5;
            //base.Height += 10;
            if (base.Height <= 0) base.Height = 5;
            if (base.Width <= 0) base.Width = 5;

            if (theXvalue != 0) theXvalue = -(theXvalue);
            if (theYvalue != 0) theYvalue = -(theYvalue);

            int i = 0;
            foreach (Point p in oldPoints)
            {

                newPoint[i].X = p.X + theXvalue;
                newPoint[i].Y = p.Y + theYvalue;
                i++;
            }
            return newPoint;
        }
        
        protected override void OnPaint(PaintEventArgs e)
        {


            base.OnPaint(e);
            e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
            e.Graphics.FillPath(b, this.path);
            e.Graphics.DrawPath(p, this.path);
            

            this.Region = new Region(this.path);
           

           
        }
        
        protected override void OnLocationChanged(EventArgs e) {
            base.OnLocationChanged(e);
            this.Invalidate();
        }

        protected override void OnResize(EventArgs e)
        {
            this.Region = new Region(path);
            this.Refresh();
            base.OnResize(e);
        }//onResize
        
    }