quoting Rhetorica, Kelatetía: Dis, Major Belt 1:

"dār" fixed (Another word that somehow got priority = 1.) Search works as long as you specify a page type; sadly the 'find all posts by this user' page doesn't do that. The issue is something heinously complicated! I will revisit it.

It's not that. In fact, testing reveals that the problematic parameter is actually name_restrict=1. Further testing shows that if that parameter is set to 0, nothing, or if it is omitted, the search function will return every forum post (but not every object on the site.) Also, the link to page 22 of any results page shows up as "happiness thread (2015-05-08 09:56:46)">22".

Even more testing reveals that the search function finally works properly if group_restrict=1 is appended to the request.