You can not use one lead to attach a horse to a fence.

If you have one lead you can not attach a horse to a fence, it requires two leads.

I expected the horse to be attached to the fence.

It would not allow me to attach the horse using the lead to the fence.

Steps to Reproduce:
1. Tame a horse (Not sure if needed)
2. Place fence and have one lead
3. Try to attach the horse to the fence with only one lead.