Thread:Project:Support desk/1.17, 1.18, 1.19, 1.20, 1.21 Critical bug - lack of translation of page name to suitable encoding - whole site is broken by update scripts (not updated)/reply (9)

But it never officially supported it. There was no feature "MediaWiki will work with broken setups". If it did, that was not intentional. You just had luck. If you are interested, you can look up the change, which broke it in SVN and see, if you can fix it again. However, I would not spend my time into fixing symptoms while I can also cure the root cause.