It has happened several times tho I'm not sure it can be reproduced on demand. Sometimes it goes very far, certainly too far for knockback. In some cases I have been unable to find the XP. Sometimes there seems to be no XP with Fire Aspect II so I started hitting a little more often. However, I have been able to find the XP pretty far away by searching nearby chambers. The area is very familiar to me. Endermen are constantly teleporting out of a water trap underground so I have many opportunities to see this. I am currently trying this without fire aspect. The point is I get the death cry and sometimes no XP near.