When searching the search request goes out via HTTPS (good), the results come back via HTTPS (still good). If no results are found the 'NO RESULTS SEARCHING ON SUBJECT "Acme Publishing" ' message is sent back via HTTP resulting is data leakage.
Having said that I think it's wonderful software. The biggest problem I find with Usenet is trying to find what I'm after and NewsBin is doing a wonderful job of indexing most groups.