Invisible Zombie Villager

After curing zombie villager and releasing from cage I was attacked by unknown invisible entity.

 

It attacked quick and moved quick like a baby zombie, but only focused me. The villager was alerted, but wasn't targeted after curing or releasing from cage. No other mob was present during the curing process. I did notice I was unable to place a block above the zombie villagers head forcing me to place it one above at a three block height.

 

The villager healed turned into a weapon Smith and it was a spawn from a zombie mob spawner/farm.