When I use negative base height for an underwater biome, it crashes

So, I wanted to create a biome called "Deep Trench", but when I set the base height to a negative value, it crashed. Not the game, the biome worked improperly. Its' edges have reached the top of the world, and its' bottom was at the bedrock.

I tried to make it less deep but still doesn't work. 

And after this, I watched the source code of the element and it wrote (-2f), but only the "2f" was green. So the game engine probably didn't understand what does the code write. So if you could say me something to solve this, that would be great.