Troubles when using i18n with book

I've got it things working as expected with 'page'-types f.i..

But with book-type nodes I've weird results:

I've got a book-structure with 5 pages under one heading.
In language1, I can for each of the 5 pages, define the parent page.
Also for each page I can create a translation.
But then... for each page in Language2 I can't define the parent (also after using 'preview' etc), as it only shows candidate pages of language1.

I've double checked that alle pages have the correct language specified, but can't make it work.

Any help appreciated.