Mobs won't attack if target isn't in the middle of a block

I can confirm this as well. It can be reproduced without even needing a /tp, if you just give yourself and the zombie a 1-wide hallway and then back up against the far wall. You'll be at the edge of the block and the zombie will keep trying to hit you without any success unless you move towards him.

Seems to be fixed in 15w45a

I do not know if this is actually the same bug, but it seems that they do not attack you, when you are in the same block they are. This can happen for example when a Skeleton is in the +X and +Z corner and you are in the -X and -Z corner

Confirmed for

• 15w49b

Reopened.

Mostly happens with baby zombies now

Confirmed in 1.9.2.

Also, if the devs are reading this, please consider nerfing baby zombies a bit. They're imba. I just died to a baby zombie in a 1v1 fight with iron boots, a gold helmet and a stone sword. They are too small and move too fast to be able to hit them consistently, especially with even the slightest amount of server lag. They've become my most feared mob, second perhaps only to witches, and because they can pop out of nowhere unexpectedly, I cannot even fight any other mobs anymore because I cannot take the risk of being blindsided in hardcore mode. It has essentially removed combat from the game for me. Now I just cower in fear in my little shelter every night. Thanks.

@unknown - see MC-50367 for baby zombies. Along with cave spiders and silverfish, the hitbox is too small on baby zombies; spam-clicking used to mask it somewhat, but with the new combat system, the tiny hitboxes on some mobs is a problem amplified by weapon cooldowns.

Confirmed for 16w14a

Please link to this comment in the description

The following is based on a decompiled version of Minecraft 1.9 using MCP 9.24 beta.

The reason for this is that the method net.minecraft.entity.ai.EntityAIAttackMelee.shouldExecute() only tests if the path to the targeted entity is not null. The problem is that if the targeted entity and the AI owner are at the same block position, the path is null.

/**
 * Returns whether the EntityAIBase should begin execution.
 */
public boolean shouldExecute()
{
    EntityLivingBase entitylivingbase = this.attacker.getAttackTarget();

    if (entitylivingbase == null)
    {
        return false;
    }
    else if (!entitylivingbase.isEntityAlive())
    {
        return false;
    }
    // Added this "else if" condition
    else if (this.attacker.getPosition().equals(entitylivingbase.getPosition())) {
        return true;
    }
    else
    {
        this.entityPathEntity = this.attacker.getNavigator().getPathToEntityLiving(entitylivingbase);
        return this.entityPathEntity != null;
    }
}

I actually hope this bug is not fixed unless part of MC-50367 (bad mob hitboxes) is fixed concurrently. In particular, baby zombies, silverfish, and cave spiders are extremely difficult to hit due to tiny hitboxes. Right now, that hitbox issue is somewhat mitigated by this bug (no melee attack if standing in same block), which causes those mobs to stand next to you, giving you an opportunity to line up your mouse exactly while your weapon is on cooldown, and finally land a hit.

In other words, in my opinion, the game is currently "better" thanks to MC-89938, but only because the game is so rage-inducingly bad as a result of parts of MC-50367.

Confirmed for 1.10.