User and group broken permissions

I created a new share called "Test"

I setup access as below in picture

ja: is member a users group

mari: member of family group

enfants: member of family group

With the below setup, enfants and mari have r/w access despite they should normally have no access at all.

If now I give the group users no access at all (I uncheck both ro and rw options), enfants will have no access at all to the share

If now I give the group users no access at all but escalate the user enfants to read only, it will correctly have a read only access

However, keep in mind, the 2 users are not members of the family group

Edit: I also tried to modify the family group permissions, they don't impact its members permissions

Again, any member, what ever is its group, it seems like it will always inherit users group permissions if they are higher than the permissions attributed to the member. The member can still escalate its own permissions above the users group permissions if we configure it to do so.

This is really a serious security issue as it doesn't behave at all as expected!