respawning farmland blocks

Fence destroyed by random farmland blocks spawning all over the place, spreading on their own and growing vegetables. Removing soil blocks, placing new blocks, jumping onto the tilled soil, none of it stops the respawn of the farmland. Placed cobblestone block and moments later it was turned to a tilled soil block and grew a carrot. Bizarre and frustrating.
edit: soil blocks are also spreading up into trees, taking over and destroying them