First timers. Read on TP that when booking the ADR and you have a dining plan it may charge you and not register your dining credits. Is this the case?
Some event-style meals require payment in advance. Cinderella's Royal Table and Hoop-dee-doo are a couple of examples. You can still use dining plan credits for them! I don't remember exactly how it works, but I do know that when you arrive at the restaurant, the server will ask if you are using the dining plan and will make sure the credits are used and any pre-paid charges to your credit card are credited.
You do have to supply a credit card for all ADRs, so it's a good idea to keep watch on all your credit card statements before and after your trip, and to hold onto receipts. It works out most of the time! I've never been charged incorrectly using the dining plan or paying out-of-pocket. Other people have occasionally experienced problems though, so keep track just in case.
From personal experience, it can happen any time you use your dining plan. We were accidentally charged for a dole whip instead of them taking snack credits, but the cast members were really nice and fixed it for us as soon as my husband went up there and let them know. We just made a habit of checking the receipt every time and saving all of them in an envelope just in case we needed them.