C++ and OpenVDB FloatGrid to Vec3SGrid and back to FloatGrid

Question

Here is a basic sample converting them and dumping the result into a mesh:

// FloatGrid  to Vec3SGrid
openvdb::Vec3SGrid::Ptr Vec3SGrid = openvdb::Vec3SGrid::create();
Vec3SGrid->setTransform( floatGridA->transformPtr());
Vec3SGrid->tree().root().setBackground(openvdb::Vec3f(floatGridA->background()),true);
for (auto itAll =  floatGridA ->cbeginValueOn(); itAll; ++itAll) {
        auto pos = itAll.getCoord();
        auto valueAll = itAll.getValue();
        auto Vec3s = Vec3SGrid->tree().getValue(pos);
        Vec3s[0] = valueAll;
        Vec3SGrid->tree().setValue(pos, Vec3s);       
 }

// Back to FloatGrid
openvdb::FloatGrid::Ptr floatGridB = openvdb::FloatGrid::create();
floatGridB->setTransform( Vec3SGrid->transformPtr());
floatGridB->tree().root().setBackground(Vec3SGrid->background()[0], true);
for (auto it = grid->cbeginValueOn(); it; ++it) {
      auto pos = it.getCoord();
      auto Vec3s = it.getValue();
       floatGridB->tree().setValue(pos, Vec3s[0]);
}
OpenVDBMesh meshA, meshB;
openvdb::tools::volumeToMesh(*floatGridA ,  meshA.points,  meshA.faces,  meshA.quads, iso, adapt, flag_relax);    
openvdb::tools::volumeToMesh(*floatGridB ,  meshB.points,  meshB.faces,  meshB.quads, iso, adapt, flag_relax);

Unfortunately the besides I've copied transform too, the result on both meshes are different.

Any idea on that? thank you!