I saw it on here, in a post, too. It's not a 'documented' feature, as I understand it.

I've also solved (in a way) the problem I mentioned above with the intensity output when saving multiple images. Basically, a dark line shows up, a single pixel thick on a horizontal and vertical edge. It's not an extra line, but is actually where data should be. So when you put the images back together, you get this dark grid. I found that, in PS, you can select a single line of pixels, either horizontally or vertically. By doing so and then choosing Filter/Other/Offset and choosing +1,+1, it pretty much hides the problem without a recognizable line remaining.