Because of nerfs I DE rares from DH, then I opened the pack and I got 9th copy of Warrior rare... Small indie company I guess.
Might be because I received the pack from Arena reward and then I DE those cards? That might be the only reasonable explanation - cards that you'll get from the pack are determined in the moment you get it and not when you open it? This system doesn't seem right.
While having already 8 copies of a rare card it's obvious that ALL rare cards were collected before DE. Everything is fine with packs system. You've failed with your first post on defending the 'is bugged' theory.
There's a caveat here: once you receive a card, you'll have it marked for "collected" purposes. So if you disenchant a card you've received, it's still considered "owned." So you can't exploit the refund system that way. There's a great benefit to this though: If you don't like a particular card or class, you can disenchant them and not have to worry about getting them in future packs. This "collected" tag lasts forever once you have collected it.
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While having already 8 copies of a rare card it's obvious that ALL rare cards were collected before DE. Everything is fine with packs system. You've failed with your first post on defending the 'is bugged' theory.
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A quote from this https://www.hearthpwn.com/news/7334-hall-of-fame-duplicate-protection-returning-player: