On my last visit to the library, I checked out 6 books. I returned 4 of them, and then a while later I renewed the other 2 online. When I did, I noticed that one of the books I had returned was listed as still being out. So, this morning, I filled out an online form to ask a question, and I told them what had happened.
I got a response back within a couple of hours from one of the librarians, saying that he had found the book "on shelf" and had removed it from my record. It's nice to see a public institution with good customer service.