My first confirmation also showed balance due by a certain date and I was given the same information when I called to check on it: don't worry about it, it's a mistake, no more money due until check-in.
I'm glad to hear I wasn't the only one on this, as I've gotten plenty of conflicting stories in planning this vacation. The very first time I called to make ressies, I got this wonderful CM who spent lots of time with me and looked for the best deal, which ended up being $79/night at PC. When I called back to make my ressies, the woman I talked to was not nearly as friendly or helpful and despite giving her the same info, dates, and so on, she kept insisting that the best deal she could give me was $89 a night. I kept asking her why it would be $10 more a night, making sure it was a standard room view, etc. Finally I just gave up and booked anyway, figuring maybe in the course of 1 day, the prices changed... turned out when I got my confirm, she had made the ressie for 3 adults in the room, instead of 2, hence an extra $10 a night fee... It's nice they keep certain info about you on file, so you don't have to give it every time, but just because my father has gone with in the past doesn't automatically mean he's going this time... And I remember her asking how many people would be in the room... very weird. It was a bit of a hassle to get this fixed, but it was taken care of and even though the woman who fixed it for me wasn't sure they could send me a new confirm, sure enough, about 4 or 5 days later, a new, correct one arrived (which showed no balance due until check-in).