Only for third parties: If you do not have the WikidataPageBanner extension installed, you probably get this error in your error logs, when a user opens your wiki in beta mode:
ErrorException from line 705 of /data/mediawiki/extensions/MobileFrontend/includes/MobileFrontend.hooks.php: PHP Warning: array_search() expects parameter 2 to be an array or collection
That's not really cool ;)
found on droidwiki.de, using MediaWiki 1.27.0-wmf.9.