LexManos, its a honor to write with a Modder like you
Only mod that changes AI is Morph Mod.
It can set so the Monsters ignor you if you are the same species.
It happend again killing a Zombie and it Crashed.
I think the Morph Mod is causing this Crash, because it changes the whole behavior of mobs.
I can send you a link to the Modpack, its a private one so i don't get sued
The link is on dropbox but i must say it only happend to me on a Server, never on Singleplayer
Hoppe that explained some things