Seeds pop back up of tilled soil/ disappear. Without a player touching them.

What I expected to happen was...:
Seeds stay and grow on tilled soil

What actually happened was...:
Seeds disappear or pop up of the tilled soil
Steps to Reproduce:
1. Till soil and get some seeds. (Large proportion
2. Place the seeds on watered tilled soil and leave them
3. Walk away and come back to see them disappear or pop up.