Since TC13.1 this behavior is changed and TC now checks the WRITE, DELETE, CREATE privileges when you do stuff with classification. By default dbas have these privileges, but not other groups/roles. So to restore previous behavior, where also being aclass_admin somewhere in the organization was enough to do all admin things in BCT aClass, users will need to update their ACLs.
Create a new ACL that gives CREATE, WRITE, DELETE privilege to the desired users for the following classes:
Has Application (ClassificationAdministratio) -> in-Class Admin Objects
---Has Class(POM_object) -> in-CLASS Admin Objects
--------Has Class(smlb0)
--------Has Class(bldb0)
--------Has Class(icm0)
--------Has Class(unct_dict)
--------Has Class(stxt)