Yea, I kind of have to rule it out too, but I went ahead and hung a cheap heater in the room as well. It turns out that they small ceramic heaters everyone is selling has a thermostat built onto the front of the unit so you can dial in a temp that you wait it to turn on at. So I pretty much set it to come on when temps get below 60. However, it doesn't seem to make a difference at all.

I think the issue is humidity to be honest and perhaps its a combination of humidity and the cold. I can see how a high humidity could cause the leaves to get damp and then when them temps drop, the leaves go crazy. Just a thought, but the plants are getting better.