/clear Max Count removes less

I was making an Adventure map Concept where if you have 64 iron, you can turn them into 1 diamond. but if you have 63 diamonds, it works aswell, which isn't what I entered.
1st Command Block:

/clear @p iron_ingot 0 64

2nd Command Block (Which gets run if the first one succeed):

/give @p diamond

Command Log:
1st Command Block:

[@: Cleared the inventory of Nusia, removing 63 items]

2nd Command Block:

[@: Given [Diamond] * 1  to Nusia]

so the bug is that it cleared my 63, even that I entered 64 as Max Count.