This is because when you convert the map's ground texture to a Pathfinding file, the file's size has to be cut in half. So a 2x2 square becomes a 1x1 square (1 pixel). And when a Pathfinding file is converted to a map's ground texture, a pixel becomes a 2x2 square.
![Image](http://img62.imageshack.us/img62/1849/imd3.jpg)
It is VERY IMPORTANT to keep this in mind because if on 2x2 square is half white and half black, you won't know if (after converting the textures to a Pathfinding file) the pixel will come out completely black or completely white.