Wither Skeletons drop coal, even if I do /gamerule domobloot false. I don't know why, but it should not drop coal. I changed the world, and the same error happens. Please fix it [Note: that bug only works for wither skeletons]

How to reproduce: Plan 1, Cheats on:

1: Get any weapon that you want, like a diamond sword, 2: Go to the Nether;

3: Do /gamerule domobloot false, 4: Find a Nether Fortress;

5: Kill the Wither Skeletons!

If you don't find a nether fortress, that's the plan 2:

1: Create a new world in Creative mode and make sure cheats is on

2: Get a diamond sword, 3: Get a wither skeleton spawn egg;

4: Do /gamerule domobloot false, and finally

5: Kill the Wither Skeletons!

Edit: I found on the Minecraft Wiki that DrownedZombie is right