Farming Wither Skeletons is a tedious business which often produces a lot of unneeded stone swords. In my survival world I sometimes try to trade these with Zombie Pigmen's golden swords in the hopes that I might get one with a decent enchantment. It worked in 1.5, when I gave a Pigman a sword and it dropped its own Fire Aspect 1 sword, which I used to de-aggro Endermen. But I tried the same thing with two naturally spawned Pigmen recently and both took the sword without dropping theirs. The first time it happened I thought it had fallen into some nearby fire, but the second time there was no fire anywhere around us.

So please fix this! And if anyone can recreate this bug in a world they play often, keep an eye out for the Pigman you gave the sword to whenever you go into the Nether, because I think there might also be a bug where these Pigmen despawn with the sword they were given.