When using a mw.Title object on a user page with a gendered namespace alias ( e.g. female Benutzerin: vs male Benutzer: on de-lang Mediwikis ) mw.Title.getNamespacePrefix() returns the default i18n namespace instead of the gendered one.
Due to that mw.Title.getPrefixedDb() differs from the output of mw.config.get( 'wgPageName' ) although it would be expected to be the same when mw.Title is created from the current page.