Contours have "cracks" at zones boundaries (partially solved)

I have an unstructured mesh Hexahedron data (I have attached a slice of the grid).

When I make contours in ParaView there are “cracks” at zones boundaries. Visit looks OK.

Any idea how this could be improved?

Edit 1 5/8 13:09:
It turns out the problem only shows up if I use different opacities for many (>5) different contours. Each contour surface is OK. But Paraview might be smartly taking into account the local grid shape, but somehow this creates the “cracks”.

Edit 5/8 13:15:
The cracks seem to be overlapping effects of different layers. So supposedly visit will have the same effects, but I don’t know to apply opacity to contour colormaps for predefined colormaps.

Edit 5/8 13:27:
I haven’t “solved” the problem. But after selecting fewer contour values the “cracks” are not very apparent, which is an acceptable result for me.