Automapping with the Tiled map editor

Automapping with the Tiled map editor

I've been trying unsuccessfully to figure out the secret behind automapping with Tiled. I would like to replace a generic 'grass' tile with other tiles depending on its neighbors. The file I uploaded (at this link http://www.mediafire.com/download/cen5e9f15003y7p/Objects.zip, since apparently I can't attach .zip files) with map2.tmx and rules.tmx describes what I've done so far; I'm trying to replace the black square in map2.tmx with the black square with a boundary. But when I automap, nothing occurs, not even an error. What could I be doing wrong?