After numerous tries, the only way that I could unassign this user relative role of parent form the UI was by manually nulling out the component entry enrol_dbuserrel' from records in the role_assign table in the database.
I guess protected roles override should be used to select whether to write the component name in the role_assign function. In my case, I was writing the component name independent of checking if roles were protected or not. Probably this was my problem?
In any case, I think I understand things a little better. How simple it would be if there was good documentation for Moodle