Assassin´s Creed II
Great question. I ran into that myself and I had (and have) no clue what to make of it, either.
Are you using the updated 1.01 version of the game? Which armor are you currently donning?
I'm running the steam copy, which I am assuming is 1.01. At present I am currently wearing mostly metal armor with the next lvl armor's (cant remember name) greves. If you have any ideas as to how to fix this, please tell me.