The 'known' bug for Butcher isn't the only one. Both an opponent and I bought and played Butcher in a game today, where the two coins were spent automatically every time we played it. This may explain the bug where you can't trash empty coppers/curses without gaining anything in return. Now it was just an overprized Remodel, and my early Quarries couldn't be converted to Militia, Talisman or Villa with coins left over. Annoying and clearly game-changing.