Just checked with firefox and IE6 and yes, it happens to me too. Sometimes I get a page with the title "Information", but the message "No topics or posts met your search criteria" isn't there, refreshing several times it finally appears, checking with the other browser (cache is new here) the message is there.
When trying another option (say last time it was 6h and now I check 12h), the same empty page appears, with both browsers, refresing a browser several times, the complete page appears, again clearing the cache and checking with the other browser the page is there.
Checking back the first option (back to search for 6h), if cached, the page was complete last time. Well, since we come from cheching for 12h, now 6h shows an empty page again.
Really strange, but it seems not related to this MOD, so I checked a normal search. Went to search.php, entered "site" (without quotes) and hit submit. Ok, it returns some posts. I refreshed the page and bang! got an empty page again!
There is something really strange here. Is it possible that you are using some kind of cache? ...or who knows. It's hard to tell. Anyway, I hope that may give you an idea or something to investigate further.