Last modified: 2013-04-22 09:50:10 UTC
In the past, MediaWiki recognizes [[Ɑ]] and [[ɑ]] two different titles, but now, [[Ɑ]] is recognized as the uppercase form of [[ɑ]], creating troubles below. This may also happen to wikis flipping $wgCapitalLinks after they've been used for a while. Original status: [[Ɑ]] is a redirect to [[ɑ]]; [[ɑ]] has contents. When [[Ɑ]] becomes the uppercase form: [[ɑ]] is never accessible directly, but accessible as a redirect target of [[Ɑ]]. After I edit [[Ɑ]]: [[ɑ]] becomes inaccessible, even if I change [[Ɑ]] back to the string "#REDIRECT [[ɑ]]" (in this case [[Ɑ]] becomes a self-redirect). To finally resolve the issue: Use api.php?action=move to move [[ɑ]] (identified by its page id) to some "ucfirst"ed title.
I don't think this is a redirect bug. The redirect just happens to exist there. Without that redirect, the bug still appears, even in a worse situation ([[ɑ]] becomes inaccessible at all).