Dirt blocks raised one level above nearby tilled dirt will fall and crush the tilled dirt, causing the tilled dirt to drop as an dirt block item.

To Reproduce
Place dirt block.
Till dirt around dirt block, one level below it.
Profit?

TerraFirmaCraft-MC1.12.2-0.29.4.119

This is consistent with falling block behavior - non full blocks will get destroyed, or (if the falling material is much softer than the block landing on), pop off as items. See #483.