I have several stamps that I use in a mod. The stamps contain a large amount of placed worldprops and some world resources.

When I go into the cartographer's table and have it randomly build a map, my stamps get included in the seed. However, the worldprops that are correctly placed in the stamp are not rotated correctly when placed in the randomized map.

http://i.imgur.com/3MvlX.jpg 

These are props that are appropriately rotated in the stamp: http://i.imgur.com/VZvry.jpg

They also show up correctly rotated when seeded in the "random map" game mode. This issue is only inside the Cartographer.