I was wandering around in the nether and I found a nether fortress. I did not have any armour. Having entered the fortress I was hit by a blaze's melee attack, then by a wither skeleton, and was killed by a blaze fireball. Later I noticed that my new iron sword was not dealing enough damage, as it was taking 10+ hits to kill a single, unarmoured skeleton. Exploring the issue further I found out that this applies to all swords, and that the amount of damage dealt on each hit varies. It can take up to 8 hits with an iron sword to kill a spider but it only ever takes 1 hit to kill a chicken, whatever sword is used. Durability is not affected, nor are bows. I have not tested swords with enchantments either. Please fix this bug as it can prove fatal in combat and I have been killed at least twice by it, and reloading the game and launcher had no effect.