A DigitalPoint Forums thread links to a story named Microsoft adCenter can't bill correctly. It goes through how the individual used a $100 promo, ran up a bill of $111 or so and was billed the whole $111 instead of just the $11 (i.e. $100 minus the $100 promo).
December 21st - Spoke to a customer service rep (CSR) who thought that I had to pay the full $111.85, and then I'd get another account credit of $100. He really wasn't sure, however, so after arguing with him on how to read an invoice, I was finally transferred to a supervisor. The supervisor told me the same exact thing that the first CSR told me about paying the full $111.85 and not $11.85.
If you want a laugh, go read that post, kinda incredible.
Forum discussion at DigitalPoint Forums.