leashes break when riding a horse

I've been testing around with horses hanging from floating fence posts. I hoped to influence the direction in which the horse "swings" without cutting the rope.
But the game won't even allow for an action like this:
As soon as the player sits on the floating horse gravity somehow pulls down both the player and the horse as if there wasn't a rope at all.

Something similar happens if you just ride away from a post the horse is tied to.

I suppose the rope shouldn't get destroyed in both cases.