Hello. I am aliasniamor on the gold server and I traded my magneton with a metal coat on it with Mirvie and as it appears, he had NOT unlocked Hoenn yet, so the magneton is now locked to him and he can't trade back. The pokemon's id is 41795970.
Mirvie told me he took screenshots of the trade/pokemon locked into his box, but I don't have any unfortunately.
If you need more information, do not hesitate to contact me via messages here on ingame. Thank you in advance !