Villagers can attempt (but never finish) to breed through a solid block and farmland which slows down basic villager farm as they rely on the sharing of food with another villager.

Steps to Reproduce:
1. create a basic 9x9 villager farm with a ceiling directly above the farmer's head.
2. create another above it with the farmland on top of the ceiling in the last step.
3. make sure a farmer is in both and is "willing" to breed.

Expected Results:
the farmers do not produce hearts and do not attempt to breed

Observed Results:
the farmers produce hearts and attempt to breed