multiple permissions on same role, and with shared root permissions

[janvp]

Following issue:
Permission A which is a parent permission.
Two children permissions B and C that inherit from A.

I have 2 roles, one that has permission B and one that has permission C.
But I also have a superadmin role that has automatically all the permissions, so it has permission A, B and C. I expected it would have all the permissions of B and C, but in fact it only had the permissions from either B or C, depending which one was inserted last in the database.