So I scraped off the cheese that hadn't started melting yet, and as much of the melted cheese as I could. The sandwich is good despite the cheese pollution. (Probably because the barbecue sauce I put on overpowers it.) Anyway, apparently we're going to have to start checking every single order with the thoroughness of a border guard from now on.
I didn't think it was too much to ask for to GET what we ORDERED, as opposed to SOMETHING ELSE. Does this make me an antiquated dinosaur who'll be swept under the rug by the relentless March Of Progress or whatever the kids are calling it nowadays?