[Paraview] beheavior

[Luis Cardon]

Dear paraview listers

Sorry to bother you with such a small thing...

I'm begining to use paraview to visualize   a numeric solution to a
simple  diffusion problem on a cubic domain. I'm plotting my initial
condition, a uniform scalar field over a cube with a smaller cube in the
center. I'm using the .vtk 2.0 file format and a RECTILINEAR GRID  data
format. My diffusion code is in fortran but I call a C subroutine to
write the .vtk files.  

 I read the file with paraview 1.4 release 3  and cut in the midle of
the cube with an implicit plane. I expect to get a square in the center
of the cutting plane. 

I observe some diffuse figure with a square resemblance but not a net
square. If I change to flat display style I get a net figure but with
saw like sides. 

Is this the expected behavior or am I doing something wrong?

Thanks very much for your time

Luis Cardón