[ether_at_cpan]

> I can't remember a time where "keys %hash" returned the keys in a defined order.

It was never a _defined_ order, but before version 5.17.6 (November 2012), each hash returned its list of keys and values in a _consistent_ order between runtimes, so some code ended up getting written that depended on this ordering (say in a unit test, or a list that would get assigned into a database). The change was to make the ordering random/inconsistent/unpredictable every time the list was fetched, which as I recall did break some number of tests in CPAN modules and required new releases.