When I was farming on my survival world i noticed that I kept falling into the water in my farms, and eventually I realised I was being dragged into the water by the farmland. So, I went into a creative mode world to test it out some more and it turns out that the farmland always pushes you off of the edge. The two videos attached demonstrate this (hopefully). To recreate, just stand on a 1x1 block of farmland and you will be pushed off.