Hash randomization in Perl 5

See Algorithmic Complexity Attacks:

In Perl 5.8.1 the hash function is randomly perturbed by a pseudorandom seed which makes generating such naughty hash keys harder. [...] but as of 5.8.2 it is only used on individual hashes if the internals detect the insertion of pathological data.

So randomization doesn't always happen, only when perl detects that it's needed.