Google uses two indexes for its search results. The normal index and the supplemental results index. Unlike the main index, from which the top results of any query comes from, supplemental search results will only show up if there are very few or no results at all in the main index. Very impressive, this always confused the hell out of me as to why your users should have cared in the first place what index the documents came from. You seem to have corrected this now I always thought it should have been transparent.