Torchflower doesn't maintain farmland used to grow it

The bug

When growing a Torchflower on Farmland, the resulting fully grown flower does not, as does the developing crop, prevent the decay of Farmland without the present of water.

Steps to reproduce

1. Place Farmland
2. Plant Torchflower seeds
3. Grow the crop until the final flower
4. Notice how Farmland decays into dirt as long as there is no water around