Whenever Cobbled Deepslate is used for, per se, crafting a furnace, the recipe is invalid—it does not work. I understand this was, at least, a sensible missing feature considering Blackstone counts as a cobblestone-variant.
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I don't think we are supposed to craft dispensers or droppers with blackstone or cobbled deepslate, by design. However, I do not have a source for this.
Relates to MC-177904
Probably WAI per this comment