Grants immunity to Stun etc.

On a few occasions, latest today, Fetter Ward has not worked. 3-5 secs after activated I'm getting slept, stunned, heavyd, bound and whatnot. Like there is some kind of latency on the effect. Any one else experience this?

On a different note, some players seems to have an eternal stun immunity. I've recognized a few players that never gets stunned (lol). Even when I sneak up and shoulder tackle them while they are on their mount. According to the game they have no immunity on, so wth?? Am I missing some mechanic here?