Yeah sorry, im playing in polish but nevertheless this is what happened to me today on arena:
I played counterfeit Blade and it got a Deathrattle of a weapon that wasnt played this game, I got it offered in discover effect but hasnt picked it nor played it. And ofc theres a wrong translations because in polish it is said about specifically MINION'S deathrattle, but well
Something weird happened to me too while playing Priest. I got a Counterfeit Blade from my opponent (because Priest antics), played it, and it gained the deathrattle of a minion I discovered but did NOT pick from Call of the Grave.
Yesterday someone otk me by using this bug with Mechathun. Mechathun wasnt dead but transformed by that new rogue spell which turns cards into stealth or pirate cards. They didnt even play Mechathun but weapon trigered its deathrattle anyways.