I'm not quite sure, but I believe what happened is that in that month, I wrote Google because I was worried about clickfraud on my site, and they said they noticed I was receiving some illigitimate traffic from a paid-to engine, so I told stopped the traffic (didn't actually know it was illigitimate to begin with) and wrote back and they thanked me... but shortly after I got a "Hi, we've noticed invalid clicks on your account, here's a warning, don't click ads, etc" kind of email, and then it was at the end of that month they audited me... kind of like they all of a sudden looked at my account and saw I had received some illigitimate traffic in past months and decided to discount that as well.
normally they do BEFRE they are shown in your account. Basically this is due to the fact that they don't want to bill AdWords users for invalid clicks..