Just played an arena game where I tried to discount Southsea Scoundrel (only Battlecry card in my hand) by swinging my Auctionhouse Gavel. Twice. Both times, no discount was applied.
It’s not just a visual bug; when I later played the Scoundrel I had to pay the full 4 mana.
See this hsreplay:
https://hsreplay.net/replay/KyVyWJY5xVPvMQkUBiq6r8 (weapon swings on turn 2 and 3; Scoundrel played on turn 5).
I guess this is probably related to these two reports: