Figure/Axes dependent patch facet visibility?

I have a patch object that I am trying to plot in an existing plot, however, for some reason some of the facets are not showing up. Here is what it looks like:

You'll notice that in the upper right hand corner it looks like a bite has been taken out of the object. However if I plot the same patch object in a new figure (and axis) I get this:

which is what it is supposed to look like (no bite missing).

I'm at a loss as to why this might be. My only guess is that its some property of the existing axis or figure, but I don't know what property I ought to be investigating. Any ideas?

[Oliver]

So it appears that the renderer is the problem. In the first figure the renderer is 'zbuffer', and if I change it to 'opengl' the problem is fixed. However, I still don't understand why 'zbuffer' would be taking bites out of my patch, any ideas why 'zbuffer' would cause this behavior?