What I actually wanted to state was that assuming Perl is not broken for some other reason that the behavior of each()

Perl is not broken here, and the documentation has a warning about inserting hash tuples whilst iterating. As I wrote, per evidence from the source, this warning is only triggered if perl is compiled with PERL_HASH_RANDOMIZE_KEYS. This doesn't mean that such operation is safe for versions that don't emit this warning.

And ceterum censeo that XS code not being able to propagate their file/lineno to perl internals is, if not a bug, an annoying lack of a basic feature that the XS subsystem should provide. (update: but see update to Re^3: To each() their own)