Holding 2 Maps Of Different Levels At Once Causes The Map Only In Main Hand To Update...

That's All...
The Steps And All That...

Ps:Try Copy This And Run It On Command Block Then Get Hit By Zombies...
So Fun...
/give @p minecraft:shield 1 12 {Unbreakable:1,ench:[

{id:0,lvl:30}

,

{id:1,lvl:30}

,

{id:4,lvl:30}

,

{id:7,lvl:30}

,

{id:19,lvl:3}

,

{id:16,lvl:4}

],HideFlags:127,display:

{Name:"Reflective Shield",Lore:[Reflection III]}

}