[vtkusers] vtkExtractEdges changes point IDs?

[David Doria]

I made a 5x5 plane source. (Throughout this discussion, I am using
paraview selection spreadsheet view to get these IDs). The ID of the
center point is 12. The ID of the point to the left of it is 11. When
I run it through vtkExtractEdges, the ID of the center point is still
12, but the point to the left of the center point changes to 10, and
other points have changed as well. Is this expected? Or a bug?

Thanks,

David