ZigZag visualization of the domain Surface
 

I'm opening a post-processed ".vtk" file of a structured grid and the domain surface is shown as a ZigZag structure instead of a rectangular one as in the first picture. This of course affect the visualization of the contour in the second picture

In the third and fourth picture I show another similar case processed with the same python code and what it looks like. It's the same paraview version mounted on the same virtual machine with ubuntu 14.

Does somebody has any idea?