Happened when turning dirt into farmland that was locking a chest.

What I expected happen was:

The chest would remain locked.

What actually happened was:

The chest became unlocked, until the farmland dried up.

Steps to reproduce:

1. Put a chest in the middle of two 2x2x1 dirt
2. Attach another dirt to the top of one of these dirt structures.
3. Right click on the dirt above the chest with a hoe.
4. Open the chest.

Farmland is a "transparent" block but it doesn't make sense why dirt blocks can lock chests but farmland can't.