It is.
For example, there’s also: I cannot finish mission"Doin' Somethin' Unholy" .
As for me, I don’t thunk I’ve made any progress casting any Shadow abilities in Mercenaries, which usually does the trick.
As already said a few times (see, for example, this: Finishing event before 'story' quests?), many of these get completed automatically just by playing enough Hearthstone in any mode even if you don’t bother with the tasks, or quests, so it’s often not a deal-breaker.