From what I have read, when a Document Structure is Released with Released Documents in the Consists of Tab, the Structure Documents are Locked. To Revise a document in the Consists of tab and Replace the previous Revision, the Parent Document Revision needs to be Revised.
When creating a New Revision, there is a statement saying You cannot replace a revision on a parent that is Released or Approved.

There is a statement saying You can always replace the revision later (manually) if you change your mind. Is this statement in regard to the previous statement regarding replacing a revision on a Parent that is Released or Approved?
Once the new subdocument is Released, On the Parent Document, on the Consists of Tab, there is an option to Replace Revision and you can replace a sub document on a Released Revision.

Is this a bug? Is there a setting to not allow any new subdocument revisions unless the Parent Document Revision is revised?
We want to lock down the revisions of the subdocuments of a Released Parent Revsion.