(This was originally reported by Joshua Delahunty via email.)
When antialiasing is enabled and a snapshot is taken that requires tiling, there are artifacts at the tile boundaries (see attached). As far as I can tell, this is caused by an ATI video driver bug, but once tiled output is updated to support more arbitrary sizes it should be possible to put margins around the tiles, and grab the tile images from inside the margins, which should hopefully make the artifacts go away.
Tiled output rendering glitch