If I craft a furnace, put either coal or a bucket of lava in and either stone, ore, or fish in the furnace, the furnace consumes the fuel but doesn't process the input.
If I'm in creative mode and I put down a furnace from the creative menu it processes inputs correctly.
I've done side by side comparisons, and the crafted furnace doesn't act the same as the creative mode furnace.
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We're tracking this issue in MC-249409, so this ticket is being resolved and linked as a duplicate.
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