As an example:
1. Create a top level document with a certain policy
2. Create a sub document with the default settings
3. Change top level document policies
4. Sub document is still set to the old policy
Instead, sub documents should default to an "Inherit" policy so that unless explicitly set, they'll always use the policy of the parent.
(I realise that setting to "Public" would probably get the same effect because of the "you must have access to parents" logic, but in the sub document's UI it'd show "Public" which would convey the wrong meaning)