Steps to reproduce:
Enable book module and configure it for article content type.
Create a node and publish it.
Create a new draft revision of the node, adding it to a book outline from the node form.
Note the node immediately appears in the book outline.
The same will be true to changes/removals from book outlines when editing nodes as draft.
There are really two bugs here:
1. Data loss/integrity due to side effects from saving drafts.
2. Access bypass on sites that have more complex workflows restricting access to publish actions, since this allows people who wouldn't be able to publish a draft to affect the published site.
1. Prevent changes to book outlines when saving revisions as drafts.
2. Add revision support to book module.
(or the first as a stop-gap and the second as a follow-up task).
A further consideration once we get to workspaces is admin/structure/book - if you're in a workspace you'd expect that to only make changes in the workspace, at the moment it'll change things on the live site.
User interface changes
Data model changes