Hmm… Still looks like degenerate geometry to me. Are you sure you are not overwriting your vertex data in some way, or getting the length of an array incorrect?
Different platforms may react in different ways to a bug in your code too.
If it is simply a simple mesh then I have never seen any bug in OpenGL on OS X that would produce that kind of blatant error. And it looks very much like the last vertex in that triangle is actually something like (0,0,0), hence the trailing triangle.
Does it happen at different locations in the grid or always the same place?
Are you using shaders? VBOs?
If the triangle mesh you have just shown is from the same data that produced the solid picture from earlier and it only does that when it’s filled and you’re truly confident that there is nothing wrong with your code then I would start looking to see if the GPU has overheating problems. Although generally a failing GPU tends to mess up filling, rather than geometry.