I may have encountered a bug in the "9 bones" minigame. I don't know if it's localized to my own personal savefile or if this issue is present in the last update or whatever, but I noticed that everytime you initiate the game, you don't spend 5 gold, you gain it. It is effectively broken, you gain 5 with a loss, 15 with a win, you just have to exit and play again every time to assure a net gain.
Most probably this is caused by the fact that when you initiate the dialogue with the NPC it says "Play '9 bones' (5 gold)", and the game reads this as "add 5 gold"; when it asks if you want to play again (second round or more) it very clearly gives you the option "Yes (-5 gold)", as in "remove 5 gold".