IGES import, unexpected results

I am interested in using OCC for the import of IGES data in order to obtain a surface triangulation of the contained root entities. These triangulations are then exported to our own proprietary formats aa a basis for FE mesh generation.
I have an IGES file which displays correctly in the sample Import/Export application. After processing I see the triangulated root entities but not arranged correctly, see fig1.bmp. The pertinant code I am using is shown below taken mainly from the elevant OCC documentation and samples.

// Read file
stat = igesReader.ReadFile(filename);
if (stat == IFSelect_RetDone ) {
myRoots = igesReader.GiveList("iges-visible-transf-roots");
nIgesRoots = myRoots->Length();
readingType = readingIges;
return(nIgesRoots);
} else {
igesReader.PrintCheckLoad(TRUE, IFSelect_ItemsByEntity);
return(0);
} /* if */
.....
// Get root entity
ent = myRoots->Value(index);
// Expand, to get any label
igesEntity = Handle(IGESData_IGESEntity)::DownCast(ent);
if (!igesEntity.IsNull()) {
if (igesEntity->HasShortLabel()) {
Handle(TCollection_HAsciiString) aLabel=igesEntity->ShortLabel();
aName = occ_string(aLabel->ToCString());
} /* if */
} /* if */
// Translate
ok = igesReader.TransferEntity(ent);
if (ok) {
TopoDS_Shape sh;
// Get the shape(s)
sh = igesReader.OneShape();
// and triangulate
BRepMesh::Mesh(sh, 1);
nt = 0;
ntri = 0;
// for each face
for (TopExp_Explorer ex(sh, TopAbs_FACE) ; ex.More(); ex.Next()) {

TopoDS_Face F = TopoDS::Face(ex.Current());
TopLoc_Location L;
Handle (Poly_Triangulation) facing = BRep_Tool::Triangulation(F,L);
TColgp_Array1OfPnt tab(1, (facing->NbNodes()));
tab = facing->Nodes();
nt = facing->NbTriangles();
Poly_Array1OfTriangle tri(1, nt);
tri = facing->Triangles();
triangles = (OccTriangle *)realloc(triangles, (nt+ntri)*sizeof(OccTriangle));
// for each triangle
for (i=1; i Poly_Triangle trian = tri.Value(i);
Standard_Integer index1,index2,index3,M,N;
trian.Get(index1,index2,index3);
gp_Pnt p;
Standard_Real x, y, z;
p = tab.Value(index1);
x = p.X(); y = p.Y(); z = p.Z();
triangles[ntri].p1.x = (float)x; triangles[ntri].p1.y = (float)y; triangles[ntri].p1.z = (float)z;
p = tab.Value(index2);
x = p.X(); y = p.Y(); z = p.Z();
triangles[ntri].p2.x = (float)x; triangles[ntri].p2.y = (float)y; triangles[ntri].p2.z = (float)z;
p = tab.Value(index3);
x = p.X(); y = p.Y(); z = p.Z();
triangles[ntri].p3.x = (float)x; triangles[ntri].p3.y = (float)y; triangles[ntri].p3.z = (float)z;
ntri++;
} /* for */
} /* for */
*nTri = ntri;
*tri = triangles;
} else {
igesReader.PrintCheckTransfer(TRUE, IFSelect_ItemsByEntity );
st = 1;
} /* if */
igesReader.PrintCheckTransfer(FALSE, IFSelect_ItemsByEntity );

I should add that the code above has workeed successfully for other IGES files.
Any help on what is going wrong would be greatly appreciated.