Can't change just one piece of armor on ArmorStands

I put in this command works perfectly:

summon ArmorStand ~ ~1 ~ {ArmorItems:[0:{id:"leather_boots",Count:1},1:{id:"leather_leggings",Count:1},2:{id:"leather_chestplate",Count:1},3:{id:"leather_helmet",Count:1}]}

Then I wanted to see if I could shorten the command, so I did this:

summon ArmorStand ~ ~1 ~ {ArmorItems:[2:{id:"leather_chestplate",Count:1}]}

Since the 2 in the top command refers to the chestplate, shouldn't the 2 in the bottom command refer to the chestplate also. The second command acts as if I wanted to change the boots and not the chestplate.

I found this when I wanted to only change one piece of armor on an armorstand.

This is also the same with entitydata also.