Oppo find 7: bootloader re-lock impossible?

I see the same behavior on my Find 7. I also seem to recall the device arriving unlocked. As far as I can tell, it simply does not support locking the bootloader.

Running unlock just instantly says OK despite the fact that Developer Options does not contain the "Enable OEM Lock" setting at all (on the latest ColorOS 2.1.5i software, which is Android 5.0 — the version where that feature was added). I also cannot find anything about (un)locking the Find 7's bootloader online other than one obscure Thai site that seems like it is probably trying to get clicks by reposting the same instructions for multiple devices.