Estoy pintando un rectángulo en los encabezados de columna en datagridview, pero al desplazarse hacia la derecha, desaparece como en la imagen (scroll.png)

aqui esta mi codigo

Rectangle r1;
void dataGridView1_Paint(object sender, PaintEventArgs e)
{
    string[] monthes = { "APPLE", "MANGO", "CHERRY", "GRAPES", "PINEAPPLE" };
    for (int j = 0; j < this.dataGridView1.ColumnCount; )
    {
        r1 = this.dataGridView1.GetCellDisplayRectangle(j, -1, true);
        int w2 = this.dataGridView1.GetCellDisplayRectangle(j + 1, -1, true).Width;
        r1.X += -2;
        r1.Y += 30;
        r1.Width = r1.Width + w2 - 1;
        r1.Height = r1.Height / 3 - 2;
        e.Graphics.FillRectangle(new SolidBrush(this.dataGridView1.ColumnHeadersDefaultCellStyle.BackColor), r1);
        StringFormat format = new StringFormat();
        format.Alignment = StringAlignment.Center;
        format.LineAlignment = StringAlignment.Center;
        e.Graphics.DrawRectangle(new Pen(Color.Black), r1);
        e.Graphics.DrawString(monthes[j / 2], this.dataGridView1.ColumnHeadersDefaultCellStyle.Font, new SolidBrush(this.dataGridView1.ColumnHeadersDefaultCellStyle.ForeColor), r1, format);

        j += 2;
    }
}

void dataGridView1_Scroll(object sender, ScrollEventArgs e)
{
    Rectangle rtHeader = this.dataGridView1.DisplayRectangle;
    rtHeader.Y += 0;
    rtHeader.Height = this.dataGridView1.ColumnHeadersHeight;
    this.dataGridView1.Invalidate(rtHeader);
}