The bug

After having farmed a crop, villagers usually don't directly pick up the harvested crops. They will either pick them up later or let them despawn.

To reproduce

1. Build a wheat field and let that field grow completely
2. Place a composter
3. Spawn a villager
4. The villager will start farming
5. It will leave harvested items on the ground

Video

https://youtu.be/HFt_6Au_7ic