Summoning an Iron Golem riding a Zombie makes the Zombie blind

Hi,

If i summon an Iron Golem riding a Zombie with the command:

    /summon VillagerGolem ~ ~1 ~ {PlayerCreated:0,NoAI:1,Silent:1,Riding:{id:"Zombie",Equipment:[{},{},{},{},{id:wool,Damage:4,Count:1}]}}

The zombie is totally blind, it doesn't focus anything: not a player, nor a villager.

Thanks

Korko