I will not have time to investigate the above travesty. Reproduced as a minimum on 5.16.2 and 5.16.3, possibly affects others. If someone is super curious and has the time - change this line to a plain $_ (pass-through): the reproduce-command is in the comment (the memlimit bashism is there to save your workstation).
^^ @haarg @ilmari @kentfredric @ap