Vengence hits way to high and hits 4 times, it's suppose to hit lower and only once.
Vengeance is what it is. It deal 3 quarter back of the official hit.
And yes.. The Vengeance spell has an endless (Infinite) loop. So if you hit him with vengeance and you also casted vengeance, it will be like this:
Example hits: 100 deal 75 back.
if you get 75 back, the other will get hitted by a 37.
and then you will get hit by a 18. Etc.