[vtkusers] change coords of a point in a Polydata

[Daniele]

Hi all,
I've a Polydata (passed under triangle filter) in which I must change
the coordinates of only a point.
If I'll set the new coordinates with

polydata->GetPoints()->SetPoint(pointID , newcoordinates);

the "new" polydata is not how I think. For example if I've a square with
9 points, and I try
to set the coordinates of the center point  I'm expecting a new polydata
like a pyramid without the base;
the new polydata instead has the base, even if the total number of
points and polys are equal before the modification.
I try to use vtkCleanPolyData but it crashes. Any ideas?

Thanks,

Dan