Block got custom NBT and is therefore no longer stackable

[Craftingdavid91]

I joined my Server with a 1.8.9 Client and interacted a bit with a stack of soul sand. After rejoining without the proxy and matching client, I realized the Soul Sand was no longer stackable. I'm not sure if this has anything to do with your proxy, just close it if you dont think so.

[RaphiMC]

This would be a ViaBackwards issue. You can report it here: https://github.com/ViaVersion/ViaBackwards/issues