Parent Group do not inherit child group contacts

To reproduce (tested on dmaster.demo.civicrm.org:
create a group 'Parent Group'
create a group 'Child Group' with parent 'Parent Group'

• add 3 contacts
  create a group 'Child Smart Group' with parent 'Parent Group'
• add different 3 contacts

Notice a few things:
On inspecting Parent Group:

• 'Child Group' contacts DO show in the list of contacts for the Parent group
• 'Child Smart Group' contacts DO NOT show in the list of contacts for the Parent group
• Neither of these groups population are reflected in the totals on the 'Manage Groups' pages (which show 0 contacts for Parent Group – expected: 6 contacts)

I'm not sure if this is the same underlying issue as here. I'm not sure if this is the same issue, or a different one, given that nothing is mentioned of the lack of contacts pulling through at the heart of this issue.