It's definitely to do with GISD, in my images, at least. Just thought that the lattice patterns could be the same thing I found. The outline of the window renders was still visible in some other situations but was really badly noticeable against a darker area of an image map bg, as you can see. The light, sky area isn't as bad.
Sorry if this isn't related, just thought that it was very similar to the problems apparent in this thread.