my old skill tree is SG, then i redistributed my skills and i chose mechanician, and i lg off and log on again, and it shows on my sham name is still SG

Did you use more skill points on SG than M, or did you use the same amount of points on both?

same points

If they're the same points, I'm pretty sure it's supposed to pick the SG. If there were more points on mech, then you should have the mech symbol