I can't remember a time where "keys %hash" returned the keys in a defined order. And I've been using Perl for over 30 years now.

I've just consulted my first issue of "Programming Perl" (printed in 1990l and it says:

keys (assoc ARRAY) this function returns a normal array consisting of all the keys of the named associative array. The keys are returned in an apparently random order, but it is the same order as either the values() or each() function produces (given that the associative array has not been modified)