I think i found a bug. I play Kerbal Space Programm in german version (via Steam)
When one of my Kerbals gets converted to a tourist due to lack of Supplies and i land him back on earth he doesnt get convertet back to his former trait. Instead his profession is calles "XP Trait" and i can no longer assign any Kerbal to any free slot. I checked my savegame and his trait was Wissenschaftler which is german for scientist. As soon as i translated it back to scientist everything was good again.
So my guess is that it is a problem with games in another language than english. And that the trait is just saved in the wrong language.
Game version: 1.7.3
Mod version: 1.2.0.0