Am I tripping, or the Furnace inside the BedRoomRoom always generates empty, even when the code says it should generate with 2+ Coals inside?

I was trying to hide some sneaky beans inside a furnace with Mixin magic, but it seems like none of the 3 slots can be filled with an item.
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Bonus bug (?): I think the same applies with Brewing stands, like the one in B-Team's Hideout.

This is the Brewing stand's block data for reference.