Alright, so I played with the stamps a little bit, and the biggest problem is that the rivers are too close to the edge of the stamp... you can see this with the curgens tomb as well. The problem with the imperium stamp is that the submerged tile gets overwritten with land and you have a waterfall tile not on a cliff.
I have mostly alleviated the problem with the Northern_Wastes. I don't see it lose it's river.
Changes:
Second round: Added Tile (26,1) to be Cliff...
Added Tile (20,0) to be Land...
Added Tile (21,0) to be Land...
Added +2 to every Y coordinate of each tile
Added +2 to every Y coordinate of each tile in MapRiverData Added
+200 to every Y coordinate for the world props. Changed TileHeight to 21 from 19
Adding the three tiles seemed to fix the problem of a land waterfall next to the river, the other fix is a biggie though as it prevents the stamps from overlapping too much and kill the river. If you want to check out the "supposed" it is located here.
https://dl.dropboxusercontent.com/u/75549875/Fallen%20Enchantress/StampFixes/S_Northern_Wastes_Blank_01_v2.zip
As for Curgen's tomb, a similar trick will prevent one river from disappearing, but then the other river disappears. Also, with the Imperium, there are times you get a land waterfall, which can be fixed probably by the same trick (haven't tried it). Note: changing the tile height without actually changing the y values causes some strange effects.
