Attacking any mob while you are not holding a weapon (an item that increases attack damage) will deal 2 damage to it, when it should be 1.

To reproduce:

1. Spawn a mob, for example, I'll use a creeper, which has 20 hp.
2. Punch it to death while counting how many times you hit it.

The creeper should die after 20 hits... But you should find that it takes 10.

Now if you do repeat the process while using a wooden shovel (which should add 1 attack damage), you'd expect it to take less than 10 hits, right?... You'll find that it still takes 10 hits.

This implies that, if without a weapon you should deal 1 damage, then weapon damage adds correctly... but without a weapon, you're dealing the same damage as with the wooden shovel, which shouldn't be correct.