Not a bug per se, but whenever the player happens to find a dragon's lair, spectral arena, hall of the sultan, etc. in a lair, and the creature is "guarding a horde of valuable spells", the player gets the choice to duel or to 'leave quietly'. As the game is now, there is not ever any reason to not give the duel a go, since the player does not lose any card if they lose the duel.

This is of course nice and profitable, especially in the early game where resources are scarce, but it would be more challenging and more of a tactical decision to duel or not if the player had ante to consider.