I found this out earlier while doing Tol Barad. I was actually the victim to this incident and decided to post it.
So what had happened is that his mage was escaping from me because of my epic dahmage and he threw down a ring before I noticed he had invised away. I saw the ring disappear when the guy went invisible and I thought that the ring was just completing its full duration. I ran through it not knowing that anything would happen and I happened to get locked down into it.
So here's the rotation, Ring of Frost and Invisibility.
It's a small bug but something you mages might enjoy when you have dots on yourself and you just wanted to make a quick escape + cc while invised.
Good luck!