Adding child book page sets parent's permissions back to default

I have several top-level books with different book access settings.

When I create a new book page, it takes the default book access settings.
However, if it's assigned to be a child of an existing book, the new book will have default permissions, and it will also set the parent and all its existing children to have the default book access permissions.

This means that every time a new child book page is created, permissions need to be reassigned to the parent book page, since it gets set back to default.