When stone trade is unlocked for stone mason villager in 1.12.0, the stone mason won't buy stone. If stone is held in hand, stone mason will display an emerald indicating willingness to trade for it, but will not accept it in the trade window. The result is the same irrespective of whether the stack is 20, 40, or 60 stone. Stone masons which unlocked stone prior to patch 1.12.0 can still trade emeralds, even after the patch. This issue only affects trades unlocked after the patch.