Glitch Summary:

When creating a superflat world (or normal world), when you reach a village, dirt or farmland blocks will begin to generate in or near a village, forming rows like the farms villages have. This will also generate crops on top of the dirt blocks. These generating blocks do not care what is in the way during generation, as houses, wells, player built blocks will be generated over. This will happen for ever, as the generation will be replacing the blocks that has already been spawned in. (Maybe fire.)

Replication:

1.  Create a new world
2.  Locate a village, or go nearby a village
3. Look for the generating blocks, which happen as soon as the chunk loads in.