I agree, those are the expected outputs. It looks to me like you may have found a bug. If you can generate and share a minimal example which reproduces the problematic behavior that would be very helpful to anyone who is trying to find the source of the problem. As it is, we are now deeper in than I will likely be able to troubleshoot. I would suggest starting a new topic (this one is marked solved so probably has less visibility) on this forum with a clean description and example of how to reproduce the issue, and also file a bug report, though it is not clear to me whether the bug is present in VMTK, Slicer, or possibly vtk. You can link back to this discussion for details on things you’ve checked already.