I probably need to go into more detail find it on other sites with more data related to this, But short and simple. Wiki says it works on opponents up to level 55. yet you can regularly land this on players 56-60 depending on MR check. I recall using this a LOT on live, in certain undead zones as a undead-only mez/CC spell. So I can't confirm if its supposed to land on undead only. But the fact its landing on people 56-60 alone seems something wrong.
I will dig up more info from other spell database and sites to prove its currently broken. Should not be able to land on a level 60 no matter what their MR is at.
http://wiki.project1999.com/Screaming_Terror