Hello,
it’s not a bug but also not really a satisfying solution. The game has a limited number of resource flags or categories to handle storage, trade and production. Altogether about 20 flags. I try to keep important resources in exclusive categories but it’s not possible in all cases. So sand is counted together with clay in one flag where all other modders have it. I find it acceptable since clay is a building material rather in early game (where sand is not used) and turns into a raw material for brickmaking later.
An alternative to handle sand together with clay is together with ores (also stored on piles being only a raw material for production like sand but of course it can confuse ore mining then. Whenever a flag is free in a future version or we get more from the developer, I will separate sand.
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