EV's lack the waste heat of an ICE to keep it dry inside. Also, It's easy to want to conserve energy to get the greatest range by minimizing climate control use. we breathe out quite a bit of moisture when we are in the car and this gradually gets soaked up by the upholstry. the car will start to even smell funky if you let this go long enough. I've found that you need to make some effort to dry out the Leaf periodically. prewarming the car in the cold wet winter helps by giving the dehymidifier/AC a chance to extract the moisture while also raising the temperature and thus the amount of moisture the air will absorb from the upholstery.
it sounds like you need to do several rounds of prewarming. if you do an 80% charge then prewarm, you will be able to do a longer prewarm... from 100% the BMS will cut short the prewarming to avoid overcharging the battery, at least in 2011-12's. I recommend cycling the prewarming a few times till you see no moisture left on the inside of the windows. once you get a feel for this, you'll develop a sense of how often it needs to be done. if you let it go too far, the amount of frost that forms on the inside of the window in the cold will get difficult to deal with. the car needs to be plugged into 240 or you will loose range while prewarming, especially as it gets really cold.