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
Place Farmland
Plant Torchflower seeds
Grow the crop until the final flower
Notice how Farmland decays into dirt as long as there is no water around
This could be fixable by making all crops use a block tag, and this block tag would be used to check whether farmland can decay naturally if something in the tag is above it.