I think this is related to the 500 message per page thing. Normally if you do a search then in the search results you can click on the result and it will take you to that particular message.
Eg if you search for posts including the phrase "wtc7" that were posted by user "snorbs" then the search results (all from the same thread) come up as expected.
Clicking through on the first of these search results works as expected by taking you to that particular post.
Clicking on the last search result doesn't work properly as it takes you to the first post of the entire thread. The only obvious difference between these search results is that the first is on page one of the thread while the last is on page two.