vtkAssembly and vtkExporter

I’m trying to export an assembly to e.g. gltf but all the positions and colors are lost. It does render correctly before exporting. Is this to be expected?

import vtk

renderer = vtk.vtkRenderer()
renderWindow = vtk.vtkRenderWindow()
renderWindow.AddRenderer(renderer)

va = cq.occ_impl.assembly.toVTK(assy)
renderer.AddActor(va);

renderWindow.Render()

exporter = vtk.vtkGLTFExporter()
exporter.SetFileName('test.gltf')
exporter.InlineDataOn() # save to single file
exporter.SetSaveNormal(False)
exporter.SetRenderWindow(renderWindow)
exporter.Write()

BTW: I’ve found this unanswered post that seems to be related: https://vtk.org/pipermail/vtkusers/2017-February/097969.html .