Sync book outline does not work

Situation:

• Activated essential modules: Book, Synchronize Translations (and dependent modules)
• Languages: en and de with language prefixes
• Created different content types for book and book pages and configured these types to form a book
• Created language independent book with three book pages.
• Then activated multilingual support for content type for books:
  • Multilingual support: enabled with translation,
  • Extended language support: normal
  • Synchronize Translations: none of the options selected
• Activated multilingual support for content type for book pages:
  • Multilingual support: enabled with translation,
  • Extended language support: normal
  • Synchronize Translations: Book outline (with the translated parent)

• First issue: I set the book to be no longer language independent (en). Then translated the book into (de). All worked well. Then set the book pages to be no longer language independent: They lost their connection to the book but became books themselves!
• Second issue: I first set the book pages to be no longer language independent (en). They retained their connection to the book! Then I set the book to be no longer language independent (en). Everything worked well! Then I translated the book into (de). Of course it had no book pages then. But it even didn't become a book parent! So I created a new book in the outline section to make this node a book parent. Then I translated the book pages into (de) expecting that the translations will automatically be assigned to the translated book (that's why I set sync book outline). But the translations didn't have a book parent! I had to manually assign the book parent.

Am I missing something?