I was opening a lot of packs for the new mercenaries, and I got a Vanndar which I already had. I opended over 110 packs and got all the mercenaries except Murloc Holmes. I think it bugged out and gave me the wrong hero!!!
this happened to me too, except mine happened around when the nagas were introduced
Was it a mercenary card or a portrait?
Regardless, I see no issue yet. See this article: https://eu.battle.net/support/en/article/32545 .
Since reading doesn’t seem to be a forte of many forum participants (modern educayshun, I guess?), let me underline a key part for you: there is only one item (out of five) in each pack that has got to do with duplicate protection and so on, the rest can give you anything — even, for example, golden portraits for legendary mercs that you own, even if some are still missing in your collection.
For further examples and illustrations, you can also watch some of these:
https://www.youtube.com/watch?v=DlsYJI5cHB0
https://www.youtube.com/watch?v=mrCEyuQBCSo
Many people got the Vanndar`s gold skin from a quest during Alterac. And later they get his standard skin in the form of a card (the same “problems” with Tyrael)
I’m aware of the situation with Vanndar (in fact, I only have his golden portrait from the event right now). And what is the problem? You can still get the base mercenary card in such situations from packs. This is also documented, by the way:
Occasionally, you may obtain a Mercenary Portrait prior to obtaining its Mercenary Card. When that happens, you will be able to play that Mercenary with the Mercenary Portrait, and you could get the Mercenary Card from packs.
As for duplicate protection in such scenarios, I haven’t seen any evidence of it not working (and, apparently, it should still apply). Have you got any?
I just explained that this is not a bug