I noticed this when I first started tracking down a problem with the CLI installer and the test runner. In the CLI installer, wgMetaNamespace is added with the value "MediaWiki", which is obviously wrong. In the web installer it gets set to the uppercased value of wgSitename and this causes the test ApiQueryTest to fail.
I'm not sure what is going on or if ApiQueryTest is wrong, but someone needs to fix something. Marking this here so I don't forget.
Version: 1.18.x
Severity: enhancement