There is different behavior between 2 objects.
For instance, on the project object, a new subobject button displays whereas a another subobject does not.
Release : 16.0.3
The following query can be used to query and compare object properties:
select a.code, a.parent_object_code, a.created_date,
a.created_by, b.user_name, a.*
from odf_objects a, cmn_sec_users b
WHERE a.created_by = b.id
and a.is_custom = 1
order by a.created_date desc;
ttran_111422 - created per 33284242