In the new pre-release 5, I have found that walking from water/waterlogged blocks onto farmland causes the player to stop as if they where walking into a barrier. 

To test this, all you need to do is place a block of water or a waterlogged slab by a farmland block and try to walk across the water and over the farmland.

See this video:

https://youtu.be/Z3muzY07IqY