I was playing the five card draw challenge, but I imagine this could happen if any circumstances caused your hand size to be small enough. I had the trading card joker. On the hook boss blind I had not discarded to destroy a card yet so trading card was still active. I played four of my five cards in hand and the hook caused the final card to be discarded, but it triggered the trading card as was destroyed. I figured that was working as intended. However it worked over and over again. It destroyed the card and payed out the $3 everytime the hook caused a single card to be discarded.
#Five card draw, the hook, and the trading card
mild orbit
ashen jetty
I encountered this bug on PC (no mods) during regular abandoned deck run.
I had 3 cards left in my hand and 0 in the deck, trading card still active. I played 2 cards as my final hand, the last one got discarded by the hook and destroyed by trading card.
I am pretty sure this not intended, since trading card talks about "first discard containing only one card" and not "the first discarded card being discarded alone"