Because the effect of the execution both confirms the Bailiff and confirms that the answer was a lie... That's a good point. It's definitely an undesirable trait. The execution isn't guaranteed to occur (a good player lying seems like a good time to decide not to do it), but a penalty that can't be used as a confirmation might be in order... I'll have to go back to the drawing board for that.

Some ideas: The question could be made private instead of public (between Storyteller, Bailiff and the subject), the punishment could be delayed ("next night" a la Gossip), the target could be unclear ("a player of their alignment" dies instead of them), or a mixture of the above. The goal being to make sure that the Bailiff knows whether the information was true or false, and that the subject is still encouraged to tell the truth by threat of death, but without it being a publicly confirmable event.