This would specifically happen if moving from one MC version that has more blockstate attributes to one with fewer. If that was done then the both blockstates would act like they were the same, screwing up the ID map.
Distant Horizons
This repo is for the Distant Horizons mod. The purpose of this submodule is to isolate code that isn't tied to a specific version of minecraft. This prevents us from having duplicate code; reducing errors and potentially helping us port to different versions faster and easier.
Check out the mod's main GitLab page here: https://gitlab.com/jeseibel/distant-horizons
source code installation
You shouldn't download this repo directly. It should be automatically included when pulling the full mod.
Open Source Acknowledgements
LZ4 for Java (data compression)
https://github.com/lz4/lz4-java
NightConfig for Json & Toml (config handling)
https://github.com/TheElectronWill/night-config
SVG Salamander for SVG support (not being used atm)
https://github.com/blackears/svgSalamander
sqlite-jdbc
https://github.com/xerial/sqlite-jdbc