This happens to me when i wanted to load a ocean world.
For some reason I have that too in 1.12.2
Dude isnt that just wrong generation?
For the desert part, thats just how it generated, for the snow biome, im not sure but i suppose that is an error.
Also thought about it being a bug or not, it is handy though in some cases
This isnt a bug since its programmed to do that like any other animal.