The Collection Extension doesn't work on the upgraded projects, giving a Javascript-alert box with an error message:
ERROR: Version mismatch between Javascript and PHP code. Contact admin to fix the installation of Collection extension for MediaWiki.
See, for example: http://nl.wikipedia.org/wiki/Speciaal:Boek or http://meta.wikimedia.org/wiki/Special:Book.
(above from [[meta:Talk:Wikimedia_maintenance_notice]]
Version: unspecified
Severity: normal