First, I paid very close attention to every part of the comparison, as to see where my ALU was off, as you said. I then realized the problem was arround my "Add16" function.
So, it actually was not off anywhere : in fact, I had created my "Add16.hdl" file in another directory, leaving the empty one inside the directory "projects/02". The software tried to use it instead of the BuiltIn one, therefore returning "0" for any "Add16" written in the program.
I took the bad file away and everything goes smooth.
I explain all this in case someone falls in the same trap as I did, sorry for the chitchat.
Thanks a lot WBahn :)