/replaceitem slot.inventory.2 confirms the 11th slot in your inventory

Update: it is really messed up for many of the slots

Confirmed.

slot.inventory starts from slot 9. slot.hotbar starts from slot 0. This is intentional.

@unknown , why is this intentional ?
In fact, the function of replaceitem slot.inventory.2 is correct, it replaces the 2nd slot of the inventory.
Same for helmet, confirmation message is slot #103.
The confirmation messages uses the internal slot numbers, see http://minecraft.gamepedia.com/Player.dat_Format#Inventory_Slot_Numbers