I have an item that I enchanted at an anvil (a sword, I think) that was given a "pushback" effect. Sometimes when I hit a monster it pushed them a few squares away from me. The error I noticed is that there was a chest that I opened, then a monster moved onto the opened chest square. When I attacked him it pushed him back and killed him. Not only did the monster get pushed back but so did the opened chest graphic.
Knockbacks are known to affect objects on the ground. People have used this to 'push' obstacles into the way of monsters and other creative uses.
you can push anything, even iron bars or traps, of course since your case is a sword it will only push stuff you can attack
