I have confirmed the situation. It can be fixed by changing line 245 in the downloaded search.asp, so that where you have
strSql2 = strSql2 & " ON F.FORUM_ID = T.FORUM_ID) INNER JOIN " & strActivePrefix & "REPLY R"
you will have
strSql2 = strSql2 & " ON F.FORUM_ID = T.FORUM_ID) LEFT JOIN " & strActivePrefix & "REPLY R"
Haven't evaluated the impact this can have on speed. I wouldn't expect it to have that much, but it has can slow it down even if a tiny little bit. I can only do some testing later. Will post the results then. I will also update the downloaded file as soon as this has been completely tested. If anyone cares to test it as well, that will be welcome.
P.S.: A very quick test showed that the page with this change was even faster for me. I can only confirm this later, however, with a more thourough test.