I registered an app today (API v2) for the first time (App ID 47, LaServ), and let it run a bit with its new key. It's the only API app running on this IP (I rent the IP as part of a VPS package). The app was making one request per minute, but every minute the quota was going down by 7. I shut the app down and refreshed the API URL manually about an hour later, and the quota was down another 1,000 or so.
What is causing my quota to decrease on its own?
I also note that on the Authorization Statistics screen for my app, it lists multiple authorizations/revocations from before the app was registered.