Thread:Extension talk:SphinxSearch/"Internal error: searchd error: unknown local index" in search results

I've just installed Sphinx 2.0.5 and SphinxSearch 0.85 on a MW 16.5 installation. (I'm trying to migrate several wikis forward from MW 1.15; I can't go to 1.19 because of an upgrade problem with 1.19 in CentOS 6.0.) The Sphinx Search function works fine, selecting appropriate results, but the screen of search results displays an error instead of the highlighted extract from the wiki for each entry found:

Sustainability/NGOs Internal error: searchd error: unknown local index 'wiki_main' in search request 11 KB (1,593 words) - 16:26, 20 July 2012

"wiki_main" is of course the default name of the wiki index in the sample sphinx.conf file. My customized sphinx.conf file no longer has an entry by that name. So where is the SphinxSearch extension picking this name up from? And is that the problem?