vtkOpenGLSphereMapper doesn't handle poly-vertex cells correctly
If a dataset contains poly-vertex cells, vtkOpenGLSphereMapper won't render it correctly.
I've attached two small sample files. One containing 4 vertex cells, the other exactly the same except that there is 1 poly-vertex cell containing two vertices, and then two vertex cells. I've also attached a small example that renders both of the files.
Here is a snapshot of the results