I am having a strange issue with nested image maps using to distribute materials on sufface.

In the above image, I have a main map which seperates the forest from the river area and trails. The nest map is use
seperate the trails from the river area. Every things works find with just the main map. The problems seem to happen once I started working with the nested map. I have rule out ecosystems and textures, by changing it to only seperation of colors.

The wierd problem is that I must scale the iamge by 341.3 ( I believe that is the value - I calculated it by 1024 / 3 ). and also offset. I could not perfectly get the offset to work because it will not let me go more than 100 in any direction.

I can probably work around with some of these because its not perfect.. But I am working a technique to make trails easy on terrains and I really would like this work.