Breeding llamas in a caravan postponed until lead removed

1. Have 4 or more llamas in a caravan.
2. Tame all llamas
3. Tie lead of first llama to a fence post
4. Give hay bales to the lead llama and the next one. A baby appears.
5. Give hay bales to the next pair of llamas (and the next pair, etc.). No babies appear.
6. Remove the lead from the first llama.
7. The remaining llamas breed and babies appear.