I've been noticing this lately. Not all of my renders are completing. Why is it that the end of images, like this, are being left out, as the render process is stopping short for some reason? I think I remember reading in the manual somewhere that if your screen is only 1600x1200 and you try to render, within the Document Window, at 2000x2000 that something will get left out, but my this is the actual size of my render, on a 1600x1200 screen. So, there was no part of the Document Window unseen before the render started.