A couple of other people on the B&N discussion boards
have been experiencing this. And some people have been getting the opposite problem, of
being retroactively charged for the promotional free books.
I wonder if they changed their system in some way. I used to get email receipts for all my $0.00 books, but now they no longer show up and some recently-joined posters have mentioned that they never get receipts for free books but always for paid.
Well, whatever's happening, I hope they get it fixed soon.