joomla/joomla-framework — pull request #314 by JoelMarcey (2013-12-14 01:40:15+00:00)
Title: Make ArrayHelperTest resilient against undefined sort order

The documentation of usort (http://us1.php.net/manual/en/function.usort.php)
makes it clear that "If two members compare as equal, their relative order in the sorted array is undefined."