MediaWiki is not compatible with PHP 5.3.1, due to http://bugs.php.net/bug.php?id=50394 . StubObject is presumably broken if you call it with reference parameters, and ParserFunctions_HookStub is reported as being definitely broken.
We need to assess the impact and possible workarounds. We may need to do a bugfix release. I will continue to work with the PHP developers to get a solution released (regardless of what Jani says).
Version: 1.15.x
Severity: major