Thread:Project:Support desk/How to search "ondiscussionpage:" ?

When I search this page I end up with an entry in the search box like "yyy ondiscussionpage:xxx" like this: http://www.mediawiki.org/w/index.php?title=Special:Search&search=search+ondiscussionpage%3AExtension+talk%3ALiquidThreads&fulltext=1&ns90=1

I don't find any information what this does exactly, where it comes from or how that functions.

I have installed LiquidThreads in my private offline wiki for testing and that search just doesn't bring any results. I can find things only via the mediawiki search box.

What can I do?