RBAC permissions not inherited by subgroup users in Casbin model

Good evening... I don't know if this is a bug or just a concept I misunderstood.
Right now, I set up a model with a combination of rbac and restful permission checks. So I created my permission sand roles, and it works perfect if I put sub users to these roles. But sadly, it doesn't work really if I use subgroups. I also checked the adapter database table and even there, there is no user entry from the groups.

Is that correct? Because from my understanding, the user from the groups should have the permissions of the role too...

groups seem have nothing to do with the Casbin model inside casdoor, you can check the code

Okay I understand. But then, why there is a field sub groups if it doens't matter?
Its just a question for understanding

no need to understand everything. it's impossible. You can't understand sth that is unrelated to you. it's just a large project with so many people's willings on it

even I don't try to do that.