Failure of member role change is not clear
A user "John" is member of the subgroup as a Developer. He is also member of the project as a Maintainer.
Problem to solve
When changing the role of John from Maintainer to Developer (in the project), this change does not happen. This is due to a policy that role project > role subgroup.
But there is no error message signaling this. Only upon refreshing the project member page, it becomes clear that the user is still Maintainer.
Notify the user that the change did not happen.