I'm having an issue with site search. First, here are the basic stats about the site.

DNN Version: 5.1.2 (No, I can't upgrade it right now.)
Two "parent" portals on the installation. Portal 0 has ~2000 pages. Portal 1 has ~50 pages. It's hosted across a load-balanced cluster, 2 servers. Database is on a separate server.
Modules: iFinity URL Master, Ultra Media Gallery, Language Extensions 1.26, several Onyaktech modules
Skins: About a dozen of them, all custom.

Here's the odd behavior I'm seeing. On the main portal (Portal 0), searching works just fine. On Portal 1 (smaller, secondary site), search always returns no results. Obviously, this isn't right. Here's what I've checked so far:

1) The scheduled search indexing is running correctly, and without errors. Indexing takes approximately 20 seconds.
2) The search terms being tested are indexed and are in the SearchWord table.
3) The GetSearchResultsByWord (@PortalID, @Word) stored proc is returning 4 results.
4) Running SQL Server Profiler during search shows that the aforementioned stored proc is being called correctly.
5) The user attempting this search has permission to view all pages. (It's a host superadmin, fer cryin' out loud!)
6) I've stepped through the source code (for 5.1.2 and 5.4.1, both) and can find no reason why there aren't 4 results returned on the search results page.

I'd like to avoid changing over to using web search for the site, since that directs people out of the site to view search results. That will be the last-ditch effort.

Also, buying another module for search is just not going to happen. If there's something for free, great. But as stated above, using web search is the last attempt, and it's free.