EDIT: It just dawned on me that each item id is being increased by 256. is this normal?
I also tested Buildcraft & some others and discovered they are doing the same thing.
industrialcraft-2_1.115.221-lf (also occurs in build 170)
Fresh install, making sure no previous ic2.cfg exists, and a brand new world.
Block ID's match the ic2.cfg file perfectly, but the Item ID's are all different.
items in ic2.cfg: 29822-30000
Actual assignment in game: 30078-30256 (despite the ID's in ic2.cfg being unused)
http://dl.dropbox.com/u/1315574/IDMap dump 21-2-2013 at 188.8.131.522.txt
As you can see, I only have Vanilla and IC² items.
What the heck is going on here?