Question about the updateFollow

Warlocks
- Warlock demons have a wide selection of names based on the demon
type. This only affects new demons; existing demons will keep their
names.
- Warlocks can no longer kill players in duels.
- Death Coil won't give health until it actually hits the target.
- Death Coil will only give the amount of health that it actually
drained from the target.
- Create Soulstone: Reduced the Soul Shard cost from two shards to one
shard.
- Curse of Shadow: Increased duration from two minutes to five minutes.
- Curse of the Elements: Increased duration from two minutes to five
minutes.
- Fear: Players now have an increasing chance to break free of the
effect, such that it is unlikely the effect will last more than 15
seconds.
- Devour Magic (Felhunter): Fixed a bug where the felhunter would be
healed every time the spell was used, in addition to the healing
gained from successful dispelling.
- Tainted Blood (Felhunter): The reactive effect no longer causes
threat.
- Training costs adjusted. Total training cost was decreased.
- Enslave Demon: Can no longer be cast on tapped targets.

Duels and PvP are different. PvP refers to killing the Alliance (if you're a Horde and vice versa). I'm guessing there was some sort of bug in the system that allowed you to kill players while duelling. I never encountered it, however.