Well when spamming the /replaceitem command (on a hat) and dropped that item (hat), it doesn't give it anymore.
Used this command with redstoneclock:
/replaceitem entity @e[team=playertwo] slot.armor.head leather_helmet 1 0 {display:{color:511},AttributeModifiers:[{operation:0,UUIDLeast:1,UUIDMost:1,Amount:-14,AttributeName:generic.maxHealth,Name:Zhead}],Unbreakable:1}
I can confirm in 14w27b. I was using a clock with this command: /replaceitem entity @a slot.hotbar.8 bow and when I removed the bow from slot 9 (8 according to command) it did not give me a new one. I did further testing and by tossing out the bow and then getting a positive comparator output off of this command: clear @p bow 0 0 I confirmed that for some reason it is giving you a ghost item or thinking you have the item even after removing it.