It's not a bug. If you line up 9 players for example and assign the 5 starters to starting + sub + reserve. In case of blowout the 4 players are still going to be used. Now the point when the coach wanted to use blowout rule your C could not be subbed but the sub was needed to put in (if you would of had 3 backup players that would have not happened) so it got put in at PG and moved to C when it was possible.