reversed triangles produced by vtkSTLWriter

Hi, I was creating vtkPolyData from points and cells. To check the result, I exported the result vtkPolyData to .stl file. And found reversed triangles in result mesh.
Here's my mesh topology.

And my code to create and export mesh to .stl file

#include <vtkVector.h>
#include <vtkTriangle.h>
#include <vtkPolyData.h>
#include <vtkSTLWriter.h>

vtkSmartPointer<vtkTriangle> GetTriangle(const int vid0, const int vid1, const int vid2)
{
    auto triangle = vtkSmartPointer<vtkTriangle>::New();

    triangle->GetPointIds()->SetId(0, vid0);
    triangle->GetPointIds()->SetId(1, vid1);
    triangle->GetPointIds()->SetId(2, vid2);

    return triangle;
}

void Test()
{
    std::vector<vtkVector3d> inputPoints(5);
    inputPoints[0] = vtkVector3d(11.97, 0, 4.75);
    inputPoints[1] = vtkVector3d(1.83, 0, 20.15);
    inputPoints[2] = vtkVector3d(9.38, 0, 11.95);
    inputPoints[3] = vtkVector3d(16, 0, 15);
    inputPoints[4] = vtkVector3d(22.73, 0, 17);

    auto points = vtkSmartPointer<vtkPoints>::New();
    for(const auto& point: inputPoints)
        points->InsertNextPoint(point.GetData());

    auto cells = vtkSmartPointer<vtkCellArray>::New();
    cells->InsertNextCell(GetTriangle(0, 1, 2));
    cells->InsertNextCell(GetTriangle(2, 1, 3));
    cells->InsertNextCell(GetTriangle(3, 1, 4));
    cells->InsertNextCell(GetTriangle(4, 2, 3));
    cells->InsertNextCell(GetTriangle(4, 0, 2));

    auto mesh = vtkSmartPointer<vtkPolyData>::New();
    mesh->SetPoints(points);
    mesh->SetPolys(cells);

    //const auto outDir = "test.stl";
    auto writer = vtkSmartPointer<vtkSTLWriter>::New();
    writer->SetFileName(outDir);
    writer->SetInputData(mesh);
    writer->Write();
}

and the result I get looks like this:

the pink triangles are reversed triangles.

Initially I thought the problem stems from wrong vertices order when creating triangle. But even if I reverse the vertices order of the reversed triangles, I still get the same result. Then I found if I export the mesh to .ply instead of .stl, I get the correct result.

I posted this in VTK discourse forum, if you want more details check this link.

Regards