Last modified: 2007-07-15 06:30:13 UTC
There is a bug in query.php that can cause it to return pi_badpageids when asked to list the contents of certain categories. I exercised this bug by empying the category that was causing the error on enwiki, [[en:Category:Stub-Class mathematics articles]], and query.php still returns the error instead of "emptyresult" at http://en.wikipedia.org/w/query.php?what=category&cptitle=Stub-Class+mathematics+articles. It has been suggested this is due to database corruption that isn't being ignored thoroughly enough.
Not sure what causes this - was not able to duplicate. Query.php is obsolete, please switch to [[mw:API]].