the very FETCH() method believes its being invoked in scalar context, even if we're trying to assign to an array.

Good. I mean: any other behaviour by Perl, in such cercumstances, would have to be considered a bug. Now, you've verified that there is no such bug.

p.s. Even if you've convinced yourself that there's no point in such experiments, I think there is: you're exploring the very corners of Perl.