Shield does not block melee attacks

The shield doesn't block melee attacks, for example. Spawn zombies and place a shield in either hand and put the survival game mode on.

What a person would expect is for the shield to block zombie attacks, but this is not the case. However, it also applies to any creature with a melee attack.

The shield luckily blocks projectiles: arrows, fireballs, etc. It is also capable of "blocking" explosions. And I say "block explosions" because the shield does not lose durability.

In short, the shield acts normal when blocking projectiles and "explosions". But melee doesn't block.