I had a mining tower with farmland preperation automation turned on. I set up the area and it worked. Deleted the tower after the area was ready to put down a farm but was unable to and the are was "marked" again for farmland preperation even after the tower was gone.

Tried adding another tower with the same area and pressing "Clear tower ATD + shift" and it removed everything. Proceded to delete the tower and still was unable to put down the farm.

Had to save and restart the game to get the are cleand up for a farm.