The lead does not leave the fence, and is invisible when it tied

What I expected to happen was that when trying to untie the tie around, it loosens up.
What really happened was that when we tie the lead on the fence, it is invisible and not be loose when trying to untie it

• Steps to reproduce: *
  1. Place a fence on the ground.
  2. Take a lead and tie a horse and fasten it on the fence.
  3. Notice that the lead was invisible depending on which direction it is looked at.
  4. Try taking the lead of the fence to untie the horse, only to realize that it is possible to take the lead destroying the fence about because the lead is not out of the fence.