Sorry for bumping, but I was looking for the solution of this problem so I reply here instead of opening another topic.
The problem with double cast happens to me too, not everytime but let's say 50% of times. I don't know if this can be avoided with changing the fps of the fight class, or other settings. So as other users said (and on other similar topics too), you can implement some C# code to prevent the double cast. But if you don't know about C# code (like me), you can use this simple lua script
Vampiric Touch cast twice
in Fight Classes assistance
Posted
Hello,
I am sorry to say that I did not make this to work.
My bot still applies Vampiric Touch twice.
I am however playing on 2.4.3 if that does any difference?