i was expecting to get a helmet with 4 armor
but when i put it on the armor bar indicates that i have 4 armor even with a
chestplate with 20 armor

Steps to Reproduce:
1. use the 2 commands: /give @p minecraft:diamond_helmet 1 0 {AttributeModifiers:[

{Slot:"head",AttributeName:"generic.armor",Name:"generic.armor",Amount:-6,Operation:0,UUIDLeast:894654,UUIDMost:2872}

,

{Slot:"head",AttributeName:"generic.armorToughness",Name:"generic.armorToughness",Amount:4,Operation:0,UUIDLeast:894654,UUIDMost:2872}

]},

/give @p minecraft:diamond_chestplate 1 0 {AttributeModifiers:[

{Slot:"chest",AttributeName:"generic.armor",Name:"generic.armor",Amount:20,Operation:0,UUIDLeast:894654,UUIDMost:2872}

,

{Slot:"chest",AttributeName:"generic.armorToughness",Name:"generic.armorToughness",Amount:4,Operation:0,UUIDLeast:894654,UUIDMost:2872}

]}
2. wear them both