The partition was on a non-removable drive, internal SSD, and it's icon was identical to the other partitions on the drive.
BTW, when I first tried to manually rename the files/folders, that were copied from a backup to the newly created JFS-partition, to their original long names it did not work. After reformatting to HPFS all seems to work fine.
Thanks for the link to filesys3.wpi, I have nothing to test it on now, so I don't know if it would have worked on the partition that didn't "accept" manual editing.
Would like to go back to JFS since it's a bit faster than HPFS, but without knowing what caused the problems in the first place I'm not sure what to do. Suspect a hardware failure so perhaps just buy a new SSD drive asap, anyone knows if there is one brand that is known to be more reliable than others?