because repair-keys is supposed to default to yes, i'd expect import-export to reorder signatures, and i'd expect an import into an empty keyring to reorder signatures.
However, it does not appear to do so.
In particular, if i strip down an OpenPGP certificate to just the smallest possible transferable public key (no subkeys, no third-party certifications, just primary key+userid+selfsig), import that thing into a keyring, and then import the full certificate again and then re-export it, the signatures do get re-ordered.
But if i just use import-export, they do not get re-ordered.
So something about the merge operation is causing repair-keys to behave differently.