Game generates Islands with mountains and hills when I Try to create single biome world using any of the Oceans as my preset. I believe this is and error with the world height where the game does not recognize the change in world high with the new update and so the water level spawns way below where it should be and thus creates hills and mountains. This is my guess as its been happening since the caves and cliffs update.

What I expected to happen was...:

A full Ocean world would be generated with no mountains or hills.

What actually happened was...:

Massive islands with hills generated and only parts of the world were oceans and even those were not deep a selected in the Deep warm ocean preset. At least in my case in the image below.

Steps to Reproduce:

1. launch Minecraft
2. Click "Create new world"
3. Chose the "Single biome" option
4. Play in the new world.