Oh, demon quest how I hate thee. Let me count the ways...
1. Getting the Winterspring demon to 10%, having the fight be perfectly under control... and then for the demon to evade bug and despawn.
2. Getting the Winterspring demon to 15%, having the fight be perfectly under control... and then for some passing idiot of a horde priest dot the target despite my yells to stay clear.
3. Getting the Burning Steppes demon to 5%, having the fight be perfectly under control... and then some horde hunter appears. Clearly unable to deal with the fact that someone else is attempting the quest instead of him, he tries to shoot the demon... but misses. That one I did get.
Basically I have been on this quest for a month. After some initial learn to play issues the Winterspring demon has been fucked up half a dozen times by bugs, idiots or griefers. So I have sympathy for the poor /cryer.