I put out the GATES OF GREENWICH series in London and I had a guy from Germany get really upset with me because he found the right ground zero, but the cache wasn't there.(It hadn't been muggled, but was most likely in the hands of other cachers when he looked.) I deleted his FOUND log because he simply hadn't found the cache. Doh. He emailed me and was quite upset. After an exchange of emails, his tone became more friendly and I allowed him to log his non-find. He was from Germany and did not expect to have another chance any time soon.
I too find it odd that anyone would think they should be able to log a cache that they haven't found - I never would - but there you go.