Magma cube Destroy shield too fast.

So i was wandering around in the nether enjoying the lovely new update.
I was wearing 3/4 iron armour half durability and a golden helmet.

This is all on my best friends server.
Anyway so i found this Giant magma cube, Size large.
And i thought i could take him on!

So i went to try, blocking his attack with my shield. Attacking him back with an iron sword.
(Nothing has enchantments btw.)

And he just SHREAD through the shields durability in mere seconds!
I heard the shield deflect noise like 100 times a second.

It just got shredded down to red durability!.

So i ran away, And hid in a hole.

Also some stuff you might wanna know:
Blue mushroom forest biome, near top of nether,
Friends server, 3/4 iron armour 1/4 gold.

I dont think it supposed to shread through like that.