Recently, I started getting back into MCD. Something I found that changed was that after killing a mob, it would sometimes get launched backwards with a trail of smoke. They get launched pretty far, off-screen most times. 

I'm not sure if this is a bug, and I think this hasn't been reported. I don't have any equipment or enchantments that give me knockback, so...

Also, I'm not sure what version I'm on, but I'm assuming it's the most recent one.

Equipment: 

Soul Crossbow w/ Anima Conduit III

Arctic Fox Armour w/ Snowball III and Death Barter III

Nightmare's Bite w/ Thundering III and Fire Aspect III