Firstly, my pumpkins still only appear in the corner of the map. I never got around to farming pumpkins in the last version of the game, so maybe that had something to do with it.
Also the lighting with the clay furnaces is weird.
Hmmm. When trying to reproduce the problem, for some reason, destroying and building new clay furnaces fixed the problem. But it was lighting up a sort of wide "square" area in front of the furnace, fading as it got further away, and it flickered like crazy. Maybe part of the reason was because there were two furnaces near each other and their lighting effects were interfering?