Villlagers wearing Thorns armour stops zombies attacking.

If villagers are wearing armour with the Thorns enchantment, when zombies attack them and are knocked back, sometimes the zombies will stop attacking, and simply stand there looking at the villager until either one is moved. It is also worth mentioning that the villagers have 100% knockback resistance.

_{Mod edit: Reinserted commands enclosed with {{{code}}} tags}
Commands for the mobs in question to save some time:

/summon Villager ~1 ~ ~ {CustomName:"Hargan",Profession:2,Offers:{Recipes:[{rewardExp:0b,maxUses:2147483647,uses:0,buy:{id:barrier,Count:1},sell:{id:barrier,Count:1}}]},ArmorItems:[{},{},{id:diamond_chestplate,Count:1,tag:{Unbreakable:1,ench:[{id:0,lvl:4},{id:7,lvl:6}]}},{}],ArmorDropChances:[0.085F,0.085F,0.0F,0.085F],Attributes:[{Name:generic.movementSpeed,Base:0.0},{Name:generic.knockbackResistance,Base:1.0}]}

/summon Zombie ~1 ~ ~ {IsBaby:0,CanBreakDoors:1,ArmorItems:[{},{},{},{id:golden_helmet,Count:1,tag:{Unbreakable:1}}],ArmorDropChances:[0.085F,0.085F,0.085F,0.0F],Attributes:[{Name:zombie.spawnReinforcements,Base:0.0F}]}