@Dammit Mainly that if the piston isn't fully opened, it doesn't auto aligned, screwing in the bolt would be a way to find out if the piston is actually opened properly.
Honestly I'm not certain, I've build up one with polymer, and serviced one with normal cable, shifting seemed to work fine (the latter have fresh lubrication in the housing).
@Dammit Mainly that if the piston isn't fully opened, it doesn't auto aligned, screwing in the bolt would be a way to find out if the piston is actually opened properly.