The mystery is solved… It’s a double action truss rod. If you need more back bow, you turn the truss rod clockwise as usual. If you turn it counterclockwise, the tension is released until you reach like a “neutral zone”, where the truss rod nut is really loose and the neck is basically dead straight. Keep turning counterclockwise and it tenses up again, but in the other direction, causing neck relief. So, crisis averted, everything works as it should and I can go ahead and try to set up the neck the way I want it.