Why do I get the diagonal lines in my mesh plot?

My code:

N= 18; % Number of cells in x- and y-direction

x=linspace(0,1,N+1); y=x;

grid_value = ones(N+1,N+1);

mesh(x,y,grid_value) view([0 0 1])

If N is larger than 17 the plot will look like: http://i40.tinypic.com/2k3kur.jpg

But if N is smaller than 17 or smaller the plot will look like: http://i39.tinypic.com/ac8xi.jpg

Where do the diagonal lines come from? And how can I remove them?

UPDATE: if I save the file as .jpg the diagonal lines disappear.

[Walter Roberson]

I seem to recall hearing of this as a bug. Which MATLAB version are you using, and which operating system?

Experiment with changing the figure renderer, such as

set(gcf, 'Renderer', 'painters')

Also experiment with the combination

set(gcf, 'Renderer', 'opengl')
opengl software