mdworker running as wrong user (macports instead of _spotlight)

I've just noticed a strange issue on an older (High Sierra) system I've nearly finished setting up – namely I'm seeing mdworker processes running as the user "macports" rather than the user I would expect "_spotlight". I'm guessing this is some kind of weird user ID mixup or something, however it's taken most of two days to copy a bunch of data onto the system, so I **really** do not want to have to wipe it and start again. As far as I can tell Spotlight is running normally, I'm guessing because the mds and mds_stores processes are running as root as normal (so can still write to my /.Spotlight-V100 folder) but this definitely doesn't seem correct. Does anyone know how I can get mdworker instances running as the correct user again, ideally without interfering with my macports installation? Though if I **have** to uninstall and reinstall macports that's not the end of the world). **Update**: In case it's relevant, I did restore one standard user from a Time Machine backup, but I specifically asked not to restore macports from that.