Search for custom namespace
Fragment of a discussion from Project:Support desk
Check this setting, and bear in mind that changes to this setting will not affect already-created accounts.
Note, as of MediaWiki 1.16, the setting will affect already existing accounts, provided that the user in question hasn't changed their search preferences from the default.
However, it sounds more like the user needs to run namespaceDupes.php maintenance script then change their search settings. Also the setting that you used for subpages won't give subpages to your newly created namespace (you list setting namespaces between 0 to 200 as having subpages, but give your new namespace the number 500)
