Farmland disappears

Put the summary of the bug you're having here
Farmland is reverting back to dirt after a few seconds, without being stepped on. This occurs in both Survival and Creative modes.

What I expected to happen was...:

I planted some seeds, and expected them to grow (over a long period of time)

What actually happened was...:
The farmland changed into dirt in a few seconds, and the planted seeds were lost.

Steps to Reproduce:
1. Use a hoe on some dirt
2. Plant melon seeds
3. Wait a few seconds