armor drop from zombies with durability being 0

when you kill a zombie with a armor there is a chanse that it will drop a armor piece with durabiliti being 0

What I expected to happen was...:
when i killed a zombie it dropped a armor piece i expected it to be like 10-15 durability 

What actually happened was...:
when i killed the zombie with gold armor it dropped but had 0 durability

Steps to Reproduce:
1. find a zombie with gold armor or wait until a mob  spawner will spawn one
2. kill the zombie
3. and there will be a chanse that it will drop a piece of armor with 0 durability