Guess it makes sense that a "collectible" Battlegrounds card would need to be a thing so that it could appear in random generation pools. Would still be nice if they were visually distinct from actually collectible cards that appear in the mode.
Still not sure how I feel about cards that involve cost in this mode, when the gameplay isn't balanced around it and it isn't a visible attribute. It would have been safer in the long run if they made some new shredders that spawn minions by tier instead of cost.
We are going to remove the rarity gem from non collectible cards. It is just a bug or oversight.