Yes, sometimes this is a tricky process and many have experienced frustration with it.
Be sure, first of all, that you are using a separate land_id for each in the <LAND_GENERATION> section. I believe for some reason or other that some numbers may not work for this. Try numbers of 10 or greater (e.g. 10, 11, 12, 13, 14), using the format:
land_id 10Next, the command is compatable with the terrain_to_place_on command, using both together is permissable and may help to reduce misplaced objects. This would work best, of course, when the terrain for each separate land is different.
What type of objects are you trying to place? If it is the starting TCs & vills, the command may not work, as the need within the program to place these things in a random spacing is probably going to override your land_id command.
Let us know if you are still having problems, more details would help us work it out.