What is material is how Perl scans the array for elements and whether those elements are stored in the array in deterministic ashion. As far as I can tell, they are.

Yes, I came to the same conclusion. It makes sense that Perl is just reading the array elements and assigns the pairs to the hash. That would be deterministic. The thing is just to really be sure that this is always the case. Highly probably it is but I just wanted to seek the wisdom of other monks.