Op, what do you think is happening? Fraud of some sort? It appears as though you have a suspicion. What is it?
Dude, I wish I knew. I had several theories but I've ruled out every single one of them, including possible problems with the CC processor/paypal integration on the site.
User interaction wise everything stays the same. Number of visitors/bounce rates/pages viewed/viewing patterns etc. are all normal. I've been checking competing websites and nothing seems unusual.