With the pumpkins problem, yeah if you'd saved it while they were in the top left corner it won't fix up. Are you able to use a sickle on them at all?
When you say "weird" lighting do you mean it's lighting up a huge area that it shouldn't be?
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?