Since BTU 1.2.1 my auto carrot and potato farms are no longer working.
The design in Unarybit's farm modified by Nathan Ryan and relies upon one block of farmland that is at a low light level to be updated by an adjacent pressure plate to break the crop and constantly attract the farming villager back to replant.

Crops will break in 0 light, but a crop planted in underneath the center of a 7x7 stone platform will not.(the platform is also surrounded by stone walls on 3 sides) even if it is updated by walking on a pressure plate.

In the attached picture, I have attempted to simulate a low light level area to see if it the crops would pop off. Since there is no F3 info available, there is no way to tell what the current light level is on the farmland block in question.