If LuceneSearch is enabled (like on Wikipedia), list=search&srwhat=nearmatch doesn't work for any titles outside main namespace (see url).
This is due to ApiQuerySearch calling $search->replacePrefixes on the search term, which is incorrect for "nearmatch" mode. LuceneSearch replaces the namespace prefixes to an internal format, so "Wikipedia:About" is transformed to "[4]:About", so the title can't be found anymore.
Version: unspecified
Severity: normal
URL: http://en.wikipedia.org/w/api.php?action=query&list=search&srwhat=nearmatch&srsearch=Wikipedia:About