Editing a top-level book page loses outline of non-book pages below it

After adding child pages to another page and editing back the main page child pages are not outlined to the main page anymore.

In order to replicate the problem and work around it, try this.

1. Create various types of content (page, blog, event whatever)
2. If there is a request to structure them and weight them, the quick fix is to create a top level book page, and then outline previously created content as child pages. They look ok in the end (book navigation block displayed on right column, pages weighted ok etc).
3. If one needs to edit top level page, after submitting/saving it, the previously outlined content (child pages) are not displayed any longer.
4. The quick work-around I have found is to click Outline tab for top level page, and simply resubmit it (no other changes - keep default top level, weight etc). As soon as the page is submitted, its children pages reappear and everything is fine. This step however should be repeated each time after one needs to edit it (step 3 above).

Additional conditions: It happens, if you create content using content types other than bookpages (so for example, page) and outline them to a book afterwards. With "real" book pages all works fine, so you might consider to repost whatever you have created, using bookpages instead other content types.