I tried to mod map generation and encountered very weird behavior of noise expressions.
Check this topic for details.
Probably there is a bug in expressions compiler.
[TOGoS] [0.16.30] Weird behavior of noise expressions
Re: [TOGoS] [0.16.30] Weird behavior of noise expressions
The "bug" was that the basis noise function was being applied to integer coordinates, which always returns 0, which isn't actually a bug.