Formation Sub Packages

So I’m using my own playbook and you can only do formation subs while in game if you run a custom playbook and I am running flexbone but want to use my backup QB because he’s mobile and I don’t want my starter getting hurt. The thing is that when I try to use the backup QB package for that formation the starting QB still stays in the game. I’m thinking that this has to be a bug. Anyone else dealing with formation sub packages while running a custom playbook or a in game playbook?