That's been happening to me a lot lately. I did the same search trying to find the thread we discussed him in this weekend but no match. I did a search on a new bot but no match and yet when I was reading thru some related pages there was the bot plain as day. Oh well.
the site search does not seem to work for all threads or all text. Also more recently added threads do not seem to be included in the search index.
try searching for: "sinner miss-spelled" and you will not find this thread.
Sometimes searching WebmasterWorld with Google will help if the subject was in the title of threads in which moderators recently posted and if Google decided to have one of their frequent spidering/short reindexing days. also see this thread: [webmasterworld.com...]
if you default visit WebmasterWorld on the recent posts [webmasterworld.com]menu (on top) and check the latest two days you tend to mostly be on top of recent postings.